I have one filed cost is 1000 and another field currencyvalue 10 and another field netcost in that i want to multiply 1000 and 10 i want 10000 answer in net cost field. how to do

decimal d3 = 0M;
if (!String.IsNullOrEmpty(TextBox2.Text.Trim()))
 Decimal.TryParse(TextBox2.Text.Trim(), out d3);
 //if (!Decimal.TryParse(TextBox2.Text.Trim(), out d3))
   //  throw new FormatException("TextBox2 - IsNullOrEmpty");

decimal d4 = 0M;
if (!String.IsNullOrEmpty(TextBox3.Text.Trim()))
 Decimal.TryParse(TextBox3.Text.Trim(), out d4);
 //if (!Decimal.TryParse(TextBox3.Text.Trim(), out d4))
   //  throw new FormatException("TextBox3 - IsNullOrEmpty");

TextBox4.Text = Convert.ToString(d3 * d4);