Here's a wicked easy way to solve it. A key thing to understand in handling many GMAT questions is the following.

If a solution works, then even if it is the easiest solution, all of the other solutions must create the same answer. For example, if an easy way to get to an answer to this question generates a way that all the songs were listened to four times, then assuming that the question was correctly designed, any other approach would give the same answer.

So if each student chooses 2 songs, all 12 songs can be chosen by 6 students choosing 2 songs each.

In order for all 12 to be chosen 4 times, that process has to happen 4 times.

6 x 4 = 24

The correct answer is D.

Thanks!

I'd opt for Brent's way: you know that 4*12 = 48 songs were picked, and each student picked two songs, so

(# of songs picked) / (# per student) = # of students

48 / 2 = 24