A retail clothing store offers customers an opportunity to open up a credit card during checkout. One location of the retail clothing store states that the number of credit cards, A, that are opened t months since January can be modeled by the function A(t) = 15 3t. The number of credit cards opened at another location, B, is defined by the function B(t) = 25 − t. 

What is an expression that can be used to determine the total amount of credit cards opened at the two locations?