Did this on the GMATprep - and I swear I got it right, but the original answer suggests differently.
2^(4-1)^2 / 2^(3-2)
I'm convinced that my answer is D (highlight to see)
But the OA is A (highlight to see)...
You can think of this two way, which are totally different. Let's just consider the top part...
This can be seen as: (2^3)^2 = 2^6
2^(3^2) = 2^9
The latter will give you the right answer. I imagine in GMATprep, it should be pretty clear. Do you have a snapshot of the problem?