When I'm stuck on a math problem, I usually find it helpful to try a simpler version of the problem to see if I can gain some insight. Suppose you went to the grocery store and you saw a special on Pringles that were 5 for $5. How much would each tube of Pringles cost? Obviously the answer is $1, but how did you know that? Which mathematical operation did you use? Now suppose you browsed the next aisle over and saw a special on 12-packs of soda, 4 for $10. How much would each 12-pack cost? Again, the answer is obviously $2.50, but how did you know that? What mathematical operation did you use? Finally, suppose the yogurt was also on sale, at 3 for $2. How much would each cup cost? Once more, the answer is obviously $0.67 (down to rounding errors...), but how did you know that? Which mathematical operation did you use?
Can you see why all four problems (the three simpler versions and your more complicated one) are fundamentally the exact same problem, just with different numbers? If you used the same operation on each of the three simpler problems (Hint: you did), it only stands to reason that the exact same operation would also be used on the more difficult problem, right? All that's changed in the more difficult problem is that the numbers don't play "nicely."