A faucet is filling a hemispherical basin of diameter 60 cm with water at a rate of 2 L/ min. Find the rate at which the water is rising in the basin when it is half full. [Use the following facts: 1 L is 1000 cm3. The volume of the portion of a sphere with radius r from the bottom to a hight h is V= π(rh2 - (1/3)h3)].