Boyle s law for gasses states that PV = constant where P is the pressure in pounds per square inch (psi) and V is the volume of the gas. For a particular gas it is known that when the pressure is 10,000 psi, its volume is 4 cubic inches. If the volume is increasing at 8 cubic inches per second, find the rate at which the pressure is changing when the pressure is 20,000 psi.