The volume of a frustum of a cone is given by the formula:
V = (1/3)Ï€h(y^2 + yz + z^2)
where y is the radius of the smaller circle, z is the radius of the larger circle, and h is the height of the frustum (see figure).
Find the rate of change of the volume of this frustum when y = 4 in, z = 2 in, and each of these dimensions is changing at the rate of 0.5 in/min.