I have no real strategy, except for that I used guess and check. How did I do this? Well, since I am in 5th Grade, I don't know algebra very well, so I made an organized chart and checked all the numbers that had to be a multiple and could be divided equally by 5, 3 and when a third of that number was subtracted by 6, it was a fifth of the orginal number. Thats how I got 45.
Checking this answer:
It is always important to check your answer after finishing the problem, so this is how I checked my answer: