Hey!
So you're kind of wanna estimate on this one,but here would be a good option:
15 - 3 = 12
Since you know that, to wanna keep adding 15 too you get 50
So 15 divided by 50 = 0.3
3 x 5 = 15
I think your final answer is going to be 15.
I really hope this helps!
Have wonderful day!! :)