Upper-level Credits Required for Dual-AOS Bachelor Degree

[csbachelor]

If you're doing a TESU bachelor's degree with two areas of study, do you need only 18 credits to be upper level for the whole degree?  Or do both areas of study need 18 upper level credits?

Take a BA in Math and Biology for example.  Not really any overlapping upper level classes in these subjects, except the capstone can be double counted.

So does this degree require 18 upper level credits, or is it (18+18 - 3 for the capstone) 33 upper level credits, split between the two subjects?