School and Work: rotating

Open Question: Find the volume of the solid obtained by rotating the region bounded by the given curves about the x-axis?

Curve y = x² and line y = 4 intersect at (-2, 4) and (2, 4)
So we integrate from x = -2 to x = 2

On this interval, line is above the curve

Each cross section perpendicular to x-axis is shaped like a washer, with
outer radius: R = 4
inner radius: r = x²

We user washer method:

V = p ??2² (R² - r²) dx
V = p ??2² (16 - x4) dx
V = p (16x - x5/5) |?2²
V = p ((32 - 32/5) - (-32 + 32/5))
V = p (64 - 64/5)
V = 256p/5

x = (3y-y^2)^(1/2)

Then also by rotating the curve about the y-axis.

I got 18piy/12y-4y^2, for about the y-axis, but webassign keeps telling me I'm wrong. Any help would be very much appreciated!!!