how do you solve 9y^18/15y^2

Answer 1

You meant "simplify".
To solve, we need an equation.

the way you typed it ...

9y^18/15y^2 = (3/5)y^20

what you probably meant:
9y^18/(15y^2) = (3y^16)/5 or (3/5)y^16

Answer 2

the answer is -6y^16