Let X~exponential(lambda).Let Y=X^.75. Compute the density of fy of Y.

The answer to this is

fY(y) = 4(lambda)(y^3)e^(-lambda*y^4) for y > 0 and equals 0 for y <= 0.

My attempt:

Y=x^0.75

dx = 4dy / x^-0.75

i then get

integral from -inf to +inf of

4(lambda)(y^3)e^(-lambda*y^4) dy

from here i don't understand how to get to the answer