using System;

using System.Text.RegularExpressions;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<string> list = new List<string>(){

      "00 1234567 89 EXT 098", 

      "001 234 56 789 EX 0987",  

      "0 0123456789 EXTEN 09",

      "00123456789 EXTENSION0987",

      "00123456789E098987" 

        };

        foreach(var item in list)

        {

string output = Regex.Replace(item, "^.*?(?=\\d+$)", "");

Console.WriteLine(output);

Console.WriteLine("********");

        }

    }

}