Calculate Hours

Hi,

Below code works  for calculate hours between  start time and end time.But i want to subtract lunch ,BF,Dinner minutes from Total hours.

 DateTime dFrom;
        DateTime dTo;
      //  DateTime val1, val2, val3;

        string sDateFrom = txt_MonStartEim.Text; 
        string sDateTo = txt_MonEndTime.Text;
         // string MonBreakfast = txt_MonBreakfast.Text;
        //string MonLunch = txt_MonLun.Text;
        //string MonDinner = txt_MonDinner.Text;
        if (DateTime.TryParse(sDateFrom, out dFrom)&& DateTime.TryParse(sDateTo, out dTo) )
        {
            TimeSpan TS = dTo - dFrom ;
           // TimeSpan TS1;
            int hour = TS.Hours;
            int mins = TS.Minutes;
            int secs = TS.Seconds;
            string timeDiff = hour.ToString("00") + ":" + mins.ToString("00") + ":" + secs.ToString("00");
           // string other = mins.ToString(mins.ToString("00") + ":" + secs.ToString("00"));
 txt_MonServiceHrs.Text = timeDiff.ToString();
}