Differentiation-rate of change

1. A cubical block of ice has an edge of 20 cm. It melts in such a way that its volume decreases at a constant rate of 25 cm^3 / s and the block remains cubical. What is the rate of change of the length of an edge when an edge is 10 cm?


2. The pressure P and volume V of a gas enclosed in a syringe are connected by the formula PV = 600.
(a) Find the rate of change of P with respect to V.
(b) V increases at 15 units per second. Find the rate of change of P when V = 20.