Pulling 2 Values From 2 Textboxes Displayed In A Third

I have a problem trying to get a value from textbox 1 and textbox 2.
If those two values match the data in the database then it has to
return a third corresponding value to a third textbox (or label) after
a user clicks a submit button. Basically, I am trying to allow users
to enter a value of weight in pounds in textbox 1 and a zip code in
textbox 2 then pulling the shipping amount from a courier's database
and returning that dollar amount to a third textbox or label after
they click submit. How would I write this code in vb.NET?

Thanks,
TG