Dynamic textboxes

Question

I am writing a math program for my grand kids. It has a dynamic panel for each add, subtraction. On the Add panel the textbox works correctly. When I add the second panel for subtraction the dynamic textbox returns an empty value. What do I need to do to get the next series of panels to accept textbox input and output? I use textbox txtboxsub = new textbox(); It works fine for the first panel. On the second panel, the textbox.text will not accept input.
Donald Blackburn