^ He is a genius. But I find it more helpful to think of it like this:
I try to balance and rearrange the equation. Your goal is to get n by itself.
If 2 things are being multiplied like (3/5)n, then you would have to put it on the opposite side of the equation being divided into what is already on that side (the right side).
n = 12 / (3/5)
since it is easier to multiply than to divide, flip the (3/5).
n = 12(5/3)
n = 60 / 3
n = 20