Perform SUM over array of objects

[lbdm]

Hi,

I need to create a rule to sum a property of an array of objects.
For example:

public class Stops(){
public string Description {get;set;}
public int Duration {get;set;}
public int Type {get;set;}
}

var array = new Stops[4];
.....

I need to write rule to sum the property Duration where Type==1 for example.
How can I do?
thanks to give me an example.
Laura