Question 1085201
This is systems of equations so lets write this out and see which method of solving works the best. Let's let children ticket amount be (c) and adult ticket amount be (a).

231 = 6c + 15a         Neither 6 nor 15 go into 231 so let's think about how to tell if a number is divisible by 6 or 15. 6 means it is divisible by 3 and 2 and 15 means it needs to be divisible by 3 and 5 so looking at 231 which is divisible by 3 (because digits add up to a multiple of 3) we can play around and tear apart this equation since a multiple of 3 stays one as long as another multiple of 3 is applied to it. So just look for two numbers within 231 that are multiples of 6 and 15

216+15=6c + 15a 

c = 36
a = 1

Sorry for the weirdest solution ever!