The answer is f(2y) = 8y^2 - 8
In order to find this, we need to put 2y in where x was in the original equation. From there, we follow the order of operations to simplify.
f(x) = 2x^2 - 8
f(2y) = 2(2y)^2 - 8
f(2y) = 2(4y^2) - 8
f(2y) = 8y^2 - 8
