diff --git a/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_1.py b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_1.py
new file mode 100644
index 0000000..8807cf6
--- /dev/null
+++ b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_1.py
@@ -0,0 +1,77 @@
+class Picture:
+    def __init__(self, colums, lines, matrix):
+        self.colums = colums
+        self.lines = lines
+        self.matrix = matrix
+
+    def check_matrix(self):
+        for i in range(0, self.colums):
+            for y in range(0, self.lines):
+                if self.matrix[i][y] < 0 or self.matrix[i][y] > 255:
+                        return False
+        return True
+
+def check_element(matrix, x, y, colums, lines, sum, flag):
+    if matrix[x][y] == 0:
+        return [[0], [0], 0]
+
+    random_point = matrix[x][y]
+    sum[0] = sum[0] + matrix[x][y]
+    flag[0] = flag[0] + 1
+    matrix[x][y] = 0
+
+    if x < (colums - 1):
+        check_element(matrix, x + 1, y, colums, lines, sum, flag)
+    
+    if  x < (colums - 1) and y < (lines - 1):
+        check_element(matrix, x + 1, y + 1, colums, lines, sum, flag)
+
+    if y < (lines - 1):
+        check_element(matrix, x, y + 1, colums, lines, sum, flag)[0]
+
+
+    return [sum, flag, random_point]
+
+def avg_brightness(picture):
+    working_matrix = picture.matrix
+    avgs = []
+    avgs_index = 0
+    
+
+    for i in range(0, picture.colums):
+        for y in range(0, picture.lines):
+            sum = [0]
+            flag = [0]
+            result = [0, 0]
+            result = check_element(working_matrix, i, y, picture.colums, picture.lines, sum, flag)
+            sum = result[0]
+            flag = result[1]
+
+            if sum[0] > 0:
+                print(f'Random point in area {avgs_index + 1} : {result[2]} \n')
+                avgs.insert(avgs_index, sum[0] / flag[0])
+                avgs_index = avgs_index + 1
+   
+    avgs.sort(reverse = True)
+
+    return avgs
+
+matrix = [[2, 2, 0, 5, 3],
+          [0, 0, 0, 3, 5],
+          [0, 0, 0, 0, 0],
+          [0, 1, 2, 3, 0],
+          [0, 0, 0, 0, 0]]
+
+p1 = Picture(5, 5, matrix)
+
+if p1.check_matrix() is False:
+    print("Invalid matrix numbers!")
+else:
+    average_p1 = avg_brightness(p1)
+
+    print("\nAverage brightness of areas:\n")
+
+    print(average_p1)
+
+    for i in range (0, len(average_p1)):
+        print(f'\nArea {i + 1} :  {average_p1[i]}\n')
\ No newline at end of file
diff --git a/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_2.py b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_2.py
new file mode 100644
index 0000000..42cbc65
--- /dev/null
+++ b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_2.py
@@ -0,0 +1,19 @@
+def num_ways(N):
+    first_num = 0
+    second_num = 1
+    ways = 0
+
+    for i in range(1, (N + 1)):
+        ways = first_num + second_num
+        first_num = second_num
+        second_num = ways
+
+    return ways
+
+stairs1 = 5
+ways_for_stairs1 = num_ways(stairs1)
+print(f'{stairs1} steps could be walked by {ways_for_stairs1} ways.\n')
+
+stairs2 = 15
+ways_for_stairs2 = num_ways(stairs2)
+print(f'{stairs2} steps could be walked by {ways_for_stairs2} ways.\n')
\ No newline at end of file
diff --git a/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_3.py b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_3.py
new file mode 100644
index 0000000..c27c320
--- /dev/null
+++ b/homeworks/04_Alexandra_Stancheva/alexandra_04_homework_2/task_3.py
@@ -0,0 +1,21 @@
+
+def replace(current_list, find, replacement):
+    for i in range(0, len(current_list)):
+        if isinstance(current_list[i], list):
+            replace(current_list[i], find, replacement)
+
+        if type(current_list[i]) is tuple:
+            new_list = list(current_list[i])
+            replace(new_list, find, replacement)
+            current_list[i] = tuple(new_list)
+
+        if current_list[i] == find:
+             current_list[i] = replacement
+
+
+
+my_list = [ 'a', 1, [ ['a', 'b'], 1], ([1, 3, 'a'], 'b')]
+
+replace(my_list, 'a', 'c')
+
+print(my_list)