using System;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

public static void Main(string[] args)

{

Demo();

Console.ReadLine();

}

public static void Demo()

{

var watch = new System.Diagnostics. Stopwatch();

watch.Start();

var task1= StartSchoolAssembly();

var task2= TeachClass12();

var task3 = TeachClass11();

Task.WaitAll(task1, task2, task3); 

watch.Stop();

Console.WriteLine("Execution Time: {0} ms", watch. ElapsedMilliseconds);

}

public static async Task StartSchoolAssembly()

{

await Task.Run(() =>

{

Thread.Sleep(8000);

Console.WriteLine("School Started");

});

}

​

public static async Task TeachClass12()

{

await Task.Run(() =>

{

Thread.Sleep(3000);

Console.WriteLine("Taught class 12");

});

}

​

public static async Task TeachClass11()

{

await Task.Run(() =>

{

Thread.Sleep(2000);

Console.WriteLine("Taught class 11");

});

}

}