using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var instr = "<td style=\"width:23.0769230769231%;\">";

        var pat = "<td style=\"width:\\d+\\.?\\d*%;\">";

        Console.WriteLine(Regex.Replace(instr, pat, "<br>"));

    }

}