New to C#.Net and need help on Number Conversion please

Question

I have 3 TextBox.

I input 123.45 into the TextBox1, input 123.22 into the TextBox2, then do a calculation (123.45 + 123.22)/2 = 123.335.

I want to display the result 123.34 instead of 123.335 in the TextBox3.

How to do that?

Appreciate for your help!