Using disks or washers, find the volume of the solid obtained by rotating the region bounded by the curves and about they-axis.

This is the graph:

So pretty much I need to find the volume of the first quadrant rotated about the y-axis, giving me a sort of upside down, round nosed cone. I'm having trouble finding the radius to substitute into my equation of the area of the circle, which I want to integrate to find the volume. Any tips/ideas?