I have been given this question and i have no idea on how to do it, any help given would be much appreciated.

A sphenical vessel is filled with water, as the level raises the radius of water in the vessel and volume changes. If radius of water in the sphere increases at 0.5cm/s. find the rate of change given volume - 4/3πr3

a) θ= (1+t2) (t-0.5)

b) x = 2cos (3t+ π/3)

Thanks you