diff --git a/lab15/t14_1.cpp b/lab15/t14_1.cpp
new file mode 100644
index 0000000..3e3d4e0
--- /dev/null
+++ b/lab15/t14_1.cpp
@@ -0,0 +1,52 @@
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <cmath>
+
+double calculateExpression(const std::vector<double>& numbers, const std::vector<char>& operators) {
+    double result = numbers[0];
+
+    for (size_t i = 0; i < operators.size(); ++i) {
+        if (operators[i] == '+') {
+            result += numbers[i + 1];
+        } else if (operators[i] == '-') {
+            result -= numbers[i + 1];
+        }
+    }
+
+    return result;
+}
+
+int main() {
+    std::ifstream inputFile("expression.txt");
+    if (!inputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для читання." << std::endl;
+        return 1;
+    }
+
+    std::string expression;
+    std::getline(inputFile, expression);
+
+    inputFile.close();
+
+    std::vector<double> numbers;
+    std::vector<char> operators;
+
+    std::istringstream iss(expression);
+    double number;
+    char op;
+
+    while (iss >> number) {
+        numbers.push_back(number);
+
+        if (iss >> op) {
+            operators.push_back(op);
+        }
+    }
+
+    double result = calculateExpression(numbers, operators);
+    std::cout << "Значення виразу: " << result << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t14_12.cpp b/lab15/t14_12.cpp
new file mode 100644
index 0000000..76b2ab6
--- /dev/null
+++ b/lab15/t14_12.cpp
@@ -0,0 +1,61 @@
+#include <iostream>
+#include <fstream>
+#include <string>
+#include <vector>
+#include <algorithm>
+
+void createAndProcessFile(const std::string& filename, int numLines) {
+    std::ofstream outputFile(filename);
+
+    if (!outputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для запису." << std::endl;
+        return;
+    }
+
+    for (int i = 0; i < numLines; ++i) {
+        std::string line = "   Line " + std::to_string(i + 1) + "   ";
+        outputFile << line << "\n";
+    }
+
+    outputFile.close();
+
+    std::ifstream inputFile(filename);
+
+    if (!inputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для читання." << std::endl;
+        return;
+    }
+
+    std::vector<std::string> lines;
+
+    std::string line;
+    while (std::getline(inputFile, line)) {
+        line.erase(std::unique(line.begin(), line.end(), [](char a, char b) { return a == ' ' && b == ' '; }), line.end());
+        line.erase(line.find_last_not_of(" \t") + 1);
+
+        lines.push_back(line);
+    }
+
+    inputFile.close();
+
+    std::ofstream editedFile(filename);
+
+    if (!editedFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для запису." << std::endl;
+        return;
+    }
+
+    for (const auto& editedLine : lines) {
+        editedFile << editedLine << "\n";
+    }
+
+    editedFile.close();
+}
+
+int main() {
+    createAndProcessFile("example.txt", 5);
+
+    std::cout << "Файл був створений та відредагований." << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t14_2.cpp b/lab15/t14_2.cpp
new file mode 100644
index 0000000..22e187a
--- /dev/null
+++ b/lab15/t14_2.cpp
@@ -0,0 +1,34 @@
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <algorithm>
+
+int main() {
+    std::ifstream inputFile("text.txt");
+    if (!inputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для читання." << std::endl;
+        return 1;
+    }
+
+    std::vector<std::string> words;
+    std::string word;
+    while (inputFile >> word) {
+        words.push_back(word);
+    }
+
+    inputFile.close();
+
+    for (size_t i = 0; i < words.size() - 2; ++i) {
+        if (words[i] == "die" || words[i] == "der" || words[i] == "das") {
+            std::transform(words[i + 2].begin(), words[i + 2].end(), words[i + 2].begin(), ::toupper);
+        }
+    }
+
+    for (const auto& w : words) {
+        std::cout << w << " ";
+    }
+    std::cout << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t14_3.cpp b/lab15/t14_3.cpp
new file mode 100644
index 0000000..f4e0d23
--- /dev/null
+++ b/lab15/t14_3.cpp
@@ -0,0 +1,51 @@
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <algorithm>
+
+std::string decryptWord(const std::string& encryptedWord) {
+    std::string decryptedWord = encryptedWord;
+    std::reverse(decryptedWord.begin(), decryptedWord.end());
+    return decryptedWord;
+}
+
+int main() {
+    std::ifstream inputFile("encrypted_text.txt");
+    if (!inputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для читання." << std::endl;
+        return 1;
+    }
+
+    std::string line;
+    std::vector<std::string> words;
+
+    while (std::getline(inputFile, line)) {
+        std::istringstream iss(line);
+        std::string word;
+
+        while (iss >> word) {
+            size_t lastCharIndex = word.find_last_of(",.!?");
+
+            if (lastCharIndex != std::string::npos) {
+                words.push_back(word.substr(0, lastCharIndex));
+                words.push_back(word.substr(lastCharIndex));
+            } else {
+                words.push_back(word);
+            }
+        }
+    }
+    inputFile.close();
+    std::ofstream outputFile("decrypted_text.txt");
+    if (!outputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для запису." << std::endl;
+        return 1;
+    }
+    for (const auto& word : words) {
+        outputFile << decryptWord(word) << " ";
+    }
+    outputFile.close();
+    std::cout << "Розшифрування завершено. Результат записано в decrypted_text.txt." << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t14_4.cpp b/lab15/t14_4.cpp
new file mode 100644
index 0000000..253498b
--- /dev/null
+++ b/lab15/t14_4.cpp
@@ -0,0 +1,47 @@
+#include <iostream>
+#include <fstream>
+#include <stack>
+
+bool checkTdTags(const std::string& line) {
+    std::stack<char> tagStack;
+
+    for (char ch : line) {
+        if (ch == '<') {
+            tagStack.push(ch);
+        } else if (ch == '>') {
+            if (!tagStack.empty() && tagStack.top() == '<') {
+                tagStack.pop();
+            } else {
+                return false;
+            }
+        }
+    }
+
+    return tagStack.empty();
+}
+
+int main() {
+    std::ifstream inputFile("your_file.txt");
+
+    if (!inputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для читання." << std::endl;
+        return 1;
+    }
+
+    std::string line;
+    int lineNumber = 0;
+
+    while (std::getline(inputFile, line)) {
+        lineNumber++;
+        if (!checkTdTags(line)) {
+            std::cout << "Помилка в рядку " << lineNumber << ": неправильна розстановка тегів <td>." << std::endl;
+            return 1;
+        }
+    }
+
+    inputFile.close();
+
+    std::cout << "Розстановка тегів <td> вірна у всіх рядках файлу." << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t14_5.cpp b/lab15/t14_5.cpp
new file mode 100644
index 0000000..eea531d
--- /dev/null
+++ b/lab15/t14_5.cpp
@@ -0,0 +1,70 @@
+#include <iostream>
+#include <fstream>
+#include <vector>
+#include <sstream>
+#include <algorithm>
+#include <limits>
+
+struct Student {
+    std::string surname;
+    int course;
+    std::string group;
+    std::vector<int> grades;
+};
+
+double calculateAverageGrade(const Student& student) {
+    if (student.grades.empty()) {
+        return 0.0;
+    }
+
+    int sum = std::accumulate(student.grades.begin(), student.grades.end(), 0);
+    return static_cast<double>(sum) / student.grades.size();
+}
+
+std::string findStudentWithLowestAverage(const std::vector<Student>& students) {
+    double lowestAverage = std::numeric_limits<double>::max();
+    std::string lowestSurname;
+
+    for (const auto& student : students) {
+        double average = calculateAverageGrade(student);
+        if (average < lowestAverage) {
+            lowestAverage = average;
+            lowestSurname = student.surname;
+        }
+    }
+
+    return lowestSurname;
+}
+
+void createStudentFile(const std::string& filename, const std::vector<Student>& students) {
+    std::ofstream outputFile(filename);
+
+    if (!outputFile.is_open()) {
+        std::cerr << "Не вдалося відкрити файл для запису." << std::endl;
+        return;
+    }
+
+    for (const auto& student : students) {
+        outputFile << student.surname << " " << student.course << " " << student.group << " ";
+        for (const auto& grade : student.grades) {
+            outputFile << grade << ",";
+        }
+        outputFile << "\n";
+    }
+
+    outputFile.close();
+}
+
+int main() {
+    std::vector<Student> students = {
+            {"Kondrashov", 2, "A1", {85, 90, 78}},
+            {"Schevchenko", 3, "B2", {92, 88, 76}},
+            {"Matseniuk", 1, "C3", {80, 95, 82}}
+    };
+
+    createStudentFile("students.txt", students);
+    std::string lowestSurname = findStudentWithLowestAverage(students);
+    std::cout << "Студент з найгіршою середньою оцінкою: " << lowestSurname << std::endl;
+
+    return 0;
+}
diff --git a/lab15/t16_1.cpp b/lab15/t16_1.cpp
new file mode 100644
index 0000000..106a4b6
--- /dev/null
+++ b/lab15/t16_1.cpp
@@ -0,0 +1,144 @@
+#include <iostream>
+#include <fstream>
+#include <string>
+
+class Person {
+    std::string name;
+    unsigned byear;
+
+public:
+    int input() {
+        std::cout << "Enter name: ";
+        std::cin >> name;
+
+        std::cout << "Enter birth year: ";
+        std::cin >> byear;
+
+        return 0;
+    }
+
+    void show() const {
+        std::cout << "Name: " << name << ", Birth Year: " << byear;
+    }
+
+    friend std::ostream& operator<<(std::ostream& os, const Person& person) {
+        os << person.name << " " << person.byear;
+        return os;
+    }
+
+    friend std::istream& operator>>(std::istream& is, Person& person) {
+        is >> person.name >> person.byear;
+        return is;
+    }
+};
+
+class Friend : public Person {
+    std::string phoneNumber;
+
+public:
+    int input() {
+        Person::input();
+
+        std::cout << "Enter phone number: ";
+        std::cin >> phoneNumber;
+
+        return 0;
+    }
+
+    void show() const {
+        Person::show();
+        std::cout << ", Phone Number: " << phoneNumber;
+    }
+
+    friend std::ostream& operator<<(std::ostream& os, const Friend& friendObj) {
+        os << static_cast<const Person&>(friendObj) << " " << friendObj.phoneNumber;
+        return os;
+    }
+
+    friend std::istream& operator>>(std::istream& is, Friend& friendObj) {
+        is >> static_cast<Person&>(friendObj) >> friendObj.phoneNumber;
+        return is;
+    }
+};
+
+class PhoneBook {
+    Friend friends[100];
+    int count;
+
+public:
+    PhoneBook() : count(0) {}
+
+    int addFriend(const Friend& friendObj) {
+        if (count < 100) {
+            friends[count++] = friendObj;
+            return 0;
+        } else {
+            return -1;
+        }
+    }
+
+    std::string findPhoneNumber(const std::string& name) const {
+        for (int i = 0; i < count; ++i) {
+            if (friends[i].name == name) {
+                return friends[i].phoneNumber;
+            }
+        }
+
+        return "Not found";
+    }
+
+    int updatePhoneNumber(const std::string& name, const std::string& newPhoneNumber) {
+        for (int i = 0; i < count; ++i) {
+            if (friends[i].name == name) {
+                friends[i].phoneNumber = newPhoneNumber;
+                return 0;
+            }
+        }
+
+        return -1;
+    }
+
+    void saveToFile(const std::string& filename) const {
+        std::ofstream outputFile(filename);
+
+        if (!outputFile.is_open()) {
+            std::cerr << "Unable to open file for writing." << std::endl;
+            return;
+        }
+
+        for (int i = 0; i < count; ++i) {
+            outputFile << friends[i] << "\n";
+        }
+
+        outputFile.close();
+    }
+};
+
+int main() {
+    PhoneBook phoneBook;
+    Friend friend1;
+    friend1.input();
+    phoneBook.addFriend(friend1)
+    Friend friend2;
+    friend2.input();
+    phoneBook.addFriend(friend2);
+    phoneBook.saveToFile("phonebook.txt");
+    std::string nameToFind = "John Doe";
+    std::string newPhoneNumber = "555-1234";
+
+    std::cout << "Phone number for " << nameToFind << ": " << phoneBook.findPhoneNumber(nameToFind) << std::endl;
+
+    if (phoneBook.updatePhoneNumber(nameToFind, newPhoneNumber) == 0) {
+        std::cout << "Phone number updated successfully." << std::endl;
+    } else {
+        std::cout << "Failed to update phone number. Entry not found." << std::endl;
+    }
+
+    std::cout << "Phonebook after update:\n";
+    for (int i = 0; i < phoneBook.getCount(); ++i) {
+        phoneBook.getFriend(i).show();
+        std::cout << std::endl;
+    }
+
+    return 0;
+}
diff --git a/lab15/t16_2.cpp b/lab15/t16_2.cpp
new file mode 100644
index 0000000..2202d26
--- /dev/null
+++ b/lab15/t16_2.cpp
@@ -0,0 +1,134 @@
+#include <iostream>
+#include <cmath>
+
+class Point {
+protected:
+    double x, y;
+
+public:
+    Point() : x(0), y(0) {}
+
+    virtual void input() {
+        std::cout << "Enter x-coordinate: ";
+        std::cin >> x;
+        std::cout << "Enter y-coordinate: ";
+        std::cin >> y;
+    }
+
+    virtual void output() const {
+        std::cout << "(" << x << ", " << y << ")";
+    }
+};
+
+class Point3D : public Point {
+protected:
+    double z;
+
+public:
+    Point3D() : z(0) {}
+
+    void input() override {
+        Point::input();
+        std::cout << "Enter z-coordinate: ";
+        std::cin >> z;
+    }
+
+    void output() const override {
+        Point::output();
+        std::cout << ", " << z;
+    }
+};
+
+class Segment {
+private:
+    Point start;
+    Point end;
+
+public:
+    Segment() {}
+
+    void input() {
+        std::cout << "Enter start point:\n";
+        start.input();
+        std::cout << "Enter end point:\n";
+        end.input();
+    }
+
+    void output() const {
+        std::cout << "Segment from ";
+        start.output();
+        std::cout << " to ";
+        end.output();
+    }
+
+    double length() const {
+        double dx = end.x - start.x;
+        double dy = end.y - start.y;
+        return std::sqrt(dx * dx + dy * dy);
+    }
+};
+
+class Segment3D {
+private:
+    Point3D start;
+    Point3D end;
+
+public:
+    Segment3D() {}
+
+    void input() {
+        std::cout << "Enter start point:\n";
+        start.input();
+        std::cout << "Enter end point:\n";
+        end.input();
+    }
+
+    void output() const {
+        std::cout << "Segment from ";
+        start.output();
+        std::cout << " to ";
+        end.output();
+    }
+
+    double length() const {
+        double dx = end.x - start.x;
+        double dy = end.y - start.y;
+        double dz = end.z - start.z;
+        return std::sqrt(dx * dx + dy * dy + dz * dz);
+    }
+};
+
+int main() {
+    Point p1;
+    Point3D p3d1;
+    Segment s1;
+    Segment3D s3d;
+
+    std::cout << "Enter 2D point:\n";
+    p1.input();
+
+    std::cout << "Enter 3D point:\n";
+    p3d1.input();
+
+    std::cout << "Enter 2D segment:\n";
+    s1.input();
+
+    std::cout << "Enter 3D segment:\n";
+    s3d.input();
+
+    std::cout << "\n2D Point:\n";
+    p1.output();
+
+    std::cout << "\n3D Point:\n";
+    p3d1.output();
+
+    std::cout << "\n2D Segment:\n";
+    s1.output();
+    std::cout << "\nLength: " << s1.length() << "\n";
+
+    std::cout << "\n3D Segment:\n";
+    s3d.output();
+    std::cout << "\nLength: " << s3d.length() << "\n";
+
+    return 0;
+}
diff --git a/lab15/t16_3.cpp b/lab15/t16_3.cpp
new file mode 100644
index 0000000..2e879be
--- /dev/null
+++ b/lab15/t16_3.cpp
@@ -0,0 +1,190 @@
+#include <iostream>
+#include <fstream>
+#include <string>
+#include <vector>
+
+class Person {
+protected:
+    std::string name;
+    unsigned byear;
+
+public:
+    Person() : byear(0) {}
+
+    virtual void input() {
+        std::cout << "Enter name: ";
+        std::cin >> name;
+        std::cout << "Enter birth year: ";
+        std::cin >> byear;
+    }
+
+    virtual void output() const {
+        std::cout << "Name: " << name << ", Birth Year: " << byear;
+    }
+
+    const std::string& getName() const {
+        return name;
+    }
+};
+
+class Passenger : public Person {
+private:
+    std::string departure;
+    std::string destination;
+    int seat;
+
+public:
+    Passenger() : seat(0) {}
+
+    void input() override {
+        Person::input();
+        std::cout << "Enter departure location: ";
+        std::cin >> departure;
+        std::cout << "Enter destination location: ";
+        std::cin >> destination;
+        std::cout << "Enter seat number: ";
+        std::cin >> seat;
+    }
+
+    void output() const override {
+        Person::output();
+        std::cout << ", Departure: " << departure << ", Destination: " << destination << ", Seat: " << seat;
+    }
+
+    int getSeat() const {
+        return seat;
+    }
+
+    const std::string& getDeparture() const {
+        return departure;
+    }
+
+    const std::string& getDestination() const {
+        return destination;
+    }
+};
+
+class Kaca {
+private:
+    std::vector<Passenger> passengers;
+
+public:
+    void addPassenger(const Passenger& passenger) {
+        passengers.push_back(passenger);
+    }
+
+    void displayPassengers() const {
+        for (const auto& passenger : passengers) {
+            passenger.output();
+            std::cout << std::endl;
+        }
+    }
+
+    const Passenger* findPassengerByName(const std::string& name) const {
+        for (const auto& passenger : passengers) {
+            if (passenger.getName() == name) {
+                return &passenger;
+            }
+        }
+        return nullptr; // Passenger not found
+    }
+
+    const Passenger* findPassengerByDeparture(const std::string& departure) const {
+        for (const auto& passenger : passengers) {
+            if (passenger.getDeparture() == departure) {
+                return &passenger;
+            }
+        }
+        return nullptr;
+
+    const Passenger* findPassengerByDestination(const std::string& destination) const {
+        for (const auto& passenger : passengers) {
+            if (passenger.getDestination() == destination) {
+                return &passenger;
+            }
+        }
+        return nullptr;
+    }
+
+    const Passenger* findAvailableSeat() const {
+        int smallestAvailableSeat = std::numeric_limits<int>::max();
+        const Passenger* availablePassenger = nullptr;
+
+        for (const auto& passenger : passengers) {
+            if (passenger.getSeat() < smallestAvailableSeat) {
+                smallestAvailableSeat = passenger.getSeat();
+            }
+        }
+
+        if (smallestAvailableSeat != std::numeric_limits<int>::max()) {
+            for (const auto& passenger : passengers) {
+                if (passenger.getSeat() == smallestAvailableSeat) {
+                    availablePassenger = &passenger;
+                    break;
+                }
+            }
+        }
+
+        return availablePassenger;
+    }
+};
+
+int main() {
+    Kaca kaca;
+
+    Passenger passenger1;
+    passenger1.input();
+    kaca.addPassenger(passenger1);
+
+    Passenger passenger2;
+    passenger2.input();
+    kaca.addPassenger(passenger2);
+
+    Passenger passenger3;
+    passenger3.input();
+    kaca.addPassenger(passenger3);
+
+    std::cout << "All Passengers:\n";
+    kaca.displayPassengers();
+
+    std::string nameToFind = "John Doe";
+    const Passenger* foundPassengerByName = kaca.findPassengerByName(nameToFind);
+    if (foundPassengerByName != nullptr) {
+        std::cout << "Passenger found by name:\n";
+        foundPassengerByName->output();
+        std::cout << std::endl;
+    } else {
+        std::cout << "Passenger with name " << nameToFind << " not found.\n";
+    }
+
+    std::string departureToFind = "CityA";
+    const Passenger* foundPassengerByDeparture = kaca.findPassengerByDeparture(departureToFind);
+    if (foundPassengerByDeparture != nullptr) {
+        std::cout << "Passenger found by departure:\n";
+        foundPassengerByDeparture->output();
+        std::cout << std::endl;
+    } else {
+        std::cout << "Passenger with departure " << departureToFind << " not found.\n";
+    }
+
+    std::string destinationToFind = "CityB";
+    const Passenger* foundPassengerByDestination = kaca.findPassengerByDestination(destinationToFind);
+    if (foundPassengerByDestination != nullptr) {
+        std::cout << "Passenger found by destination:\n";
+        foundPassengerByDestination->output();
+        std::cout << std::endl;
+    } else {
+        std::cout << "Passenger with destination " << destinationToFind << " not found.\n";
+    }
+
+    const Passenger* availableSeat = kaca.findAvailableSeat();
+    if (availableSeat != nullptr) {
+        std::cout << "Available seat found:\n";
+        availableSeat->output();
+        std::cout << std::endl;
+    } else {
+        std::cout << "No available seat found.\n";
+    }
+
+    return 0;
+}