The simplest way I can explain* is for these types of problems, all you do is make an equation like the one above and use an X as the numerator in the second equation over the denominator, which should be something like 120 in this problem. So after you find the information for the problem, which is the part where it states how much time a line of 48 people had to wait, make an equation using that information, which is 12/48. Then to finish the equation, use the 120 people in line part and make another equation that has an X as the numerator, or the number on top. It should look like this:
