using System;
using System.Collections.Generic;
using System.Linq;

namespace TestThat
{
    class MainClass
    {
        public static void Main (string[] args)
        {
			var theList = new [] {
				new { PartNumber="FID34" }
			};
			
			var result = theList
				.Where (line => line.PartNumber.StartsWith("FID", StringComparison.CurrentCultureIgnoreCase))
				.OrderBy (line =>
					{	
						int pnumber;
						return Int32.TryParse(line.PartNumber.Substring(3), out pnumber)
							? pnumber 
							: 0;
					});

        }
    }
}