Let A and B represent the unknown numbers. The bank safe combination is of the form 15-A-B.
The variables A and B multiply to 24, so AB = 24 is the equation to set up.
Here's the entire set of possible A,B values dealing with positive integers only.
Since a combination like 15-4-6 is different from 15-6-4, this means the solution (A,B) = (4,6) is different from (A,B) = (6,4). Overall, the order matters in this bank safe combination.