Well, I find this problem to be very interesting for meta-math reasons. It illustrates what we are all up against as the SAT changes. When I looked at it, I thought: OK, this is a system of 2 equations and 2 unknowns. The math teacher side of me knows how to solve those and then you can plug in to the expression…but the SAT teacher sees the expression and suspects that there is an easy work-around. It used to be something you could rely on – that seemingly weird requests to evaluate random-seeming expressions where actually an invitation to a shortcut. But now, we just don’t have enough data to know if the rules have changed. So this time, it may save time to just go ahead and solve the system.
For the record, I have never seen a current-style actual SAT problem that requires a simultaneous solution of a system of 2 eqns. There has always been a work-around. But now we have to wait and see…