a cylinder is cut from a solid sphere of radius 3cm. given that the cylinder has height 2h, find its radius in terms of h. hence show that the volume V cubic centimetres of the cylinder is given by

V = 2 x pi x h (9 - h^2)

now this has me stuck bcos i would have tried to find a relation between r and h by using the formula for V. but since this is ruled out, i really have no idea where to start.