Hello Dan,
How about using JavaScript? Why would you want to handle this on the server side instead of client side? JavaScript is a great language for computations, conditions, and a several thousand other tasks
I would recommend using the following JavaScript within your form.
Here is my hypothetical example:
Field 1 Shortfieldname = 'Field1'
Field 2 Shortfieldname = 'Field2'
So the JavaScript would need to go into the on Client Side section under Advanced Question Options for the 'Field1' question.
The JavaScript could be like this:
if($(Field1) == 'US')
{
$(Field2) = '8';
}
else if($(Field1) != 'US')
{
$(Field2) = '10';
}
else
{
$(Field2) = '';
}
Let me know if this helps.
-Ryan