(C#) I need to multiply the price and qty in datagridview?

Hi all! I meed to multiply the price and tqy in datagridview to display the sum to third cell on currentrow. I my default price is 0.0 so I give the new value to it and the default qty is 1. After I am changimg the price to new value I press Enter key on keyboard or press allow next on keyboard I need the price automatically sum to third cell. How do I do it and which event I put the source code to. I new user in developing C# winform. Thank so much.