Program.cs
 

using System;
using System.Linq;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int[] myNumbers = {5, 1, 8, 9};
      Console.WriteLine(myNumbers.Max());  // largest value
      Console.WriteLine(myNumbers.Min());  // smallest value
      Console.WriteLine(myNumbers.Sum());  // sum of myNumbers
    }
  }
}

Result:
9
1
23