using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var p = new[]

        {

            Diff(Time(7, 28), Time(11, 30)),

            Diff(Time(12, 30), Time(18, 28)),

            Diff(Time(18, 29), Time(20, 20)),

            Diff(Time(21, 30), Time(22, 36)),

        };

        for (int i = 0; i < p.Length; i++)

        {

            Console.WriteLine($"P{i + 1} = {p[i]:hh':'mm}");

        }

        var total = p.Aggregate(TimeSpan.Zero, (a, b) => a + b);

        Console.WriteLine($"T  = {total:hh':'mm}");

    }

    private static TimeSpan Diff(TimeSpan t1, TimeSpan t2) => t2 - t1;

    private static TimeSpan Time(int h, int m) => new TimeSpan(h, m, 0);

}