I wouldn't even know where to begin with this problem. Any suggestions?
The volume of a right circular cone is It looks like you almost had it, but the given radius is not
If you want to derive the formula, an easy way to do it is to position a right triangle such that its right angle is at the origin and its two legs along the - and -axes, and find the volume of the solid resulting from revolving the triangular region about one of the axes.