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? (a b)(t) = 40 4t (a b)(t) = 40 2t (a − b)(t) = −10 2t (a − b)(t) = −10 4t