water is flowing at the rate of 6 m^3.min from a reservoir shaped like a hemispherical bowl of radius 13 m, shown here in profile. Answer the following questions, given that the volume of water in a hemisphrical bowl of radius R is V = (pie/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?

Question

water is flowing at the rate of 6 m^3.min from a reservoir shaped like a hemispherical bowl of radius 13 m, shown here in profile. Answer the following questions, given that the volume of water in a hemisphrical bowl of radius R is V = (pie/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?