I want to get the balance leave

Question

i have following fields in the application as follows;

Eligibility Leave       36   Texbox1

Availed  Leave         3    Textbox2

Balance                  33    Textbox3

when i type availed leave 3 in Textbox2  i want the output as 33(Balance).

 private void txt_availed_TextChanged(object sender, EventArgs e)

        {

         

        }

Please help me.