using System;

using System.Drawing;

using System.Linq;

using System.Collections.Generic;

​

public class ListClass 

{

    public ListClass(int x, int y)

    {

        X = x;

        Y = y;

    }

    public int X { get; set; }

    public int Y { get; set; }

}

public class Program

{

    public static void Main()

    {

​

        var listA = new int [] {5,4,1,2,7,3,8,6};

        var listB = new List<ListClass>

        {

            new ListClass(1,20),

            new ListClass(4,11),

            new ListClass(7,5)

        };

        var results = listB.OrderBy

            (

                p => Array.IndexOf(listA, p.X)

            );

        foreach (var r in results) Console.WriteLine("{0},{1}", r.X, r.Y);

    }

}