this is one where you have to draw a diagram. It uses mostly math intuition instead of formulas and such. draw a rectangular solid in 3-D and write in the areas 15, 24, and 40 on the three faces. after staring for a few seconds, you can see that the only sides that make sense are 3,5, and 8. bc 3x5=15 8x3=24 and 5x8=40. and these can be set up to be adjacent as they are in the stimulus. so the answer is 3x5x8=120
PS Answer: 120
However, since 15 and 24 have two common factors, 3 and 1, just saying that they are adjacent does not do the trick (whereas two prime numbers would, like 7 and 5) so you cant predict the common side of the faces with just (1), so the third area must be known, where (2) gives you this information. And also these are the only sides that can be used to create the three areas in this manner.
DS Answer: C