Related Rates of Change: Draining a Hemispherical Reservoir

Water is flowing at the rate of 6 m^3 /min from a reservoir shaped like a hemispherical bowl of radius 13 m. Answer the following questions, given that the volume of water in a hemispherical bowl of radius R is
V = ( pi /3)y^2 (3R - y) when the water is y meters deep.
a) At what rate is the water level changing when the water is 8 m deep?
b) What is the radius r of the water’s surface when the water is y m deep?
c) At what rate is the radius r changing when the water is 8 m deep?