Rate of increase of air pressure in a compressed syringe from a constant product of pressure and volume

Air is sealed inside a syringe, and the plunger is pushed in so that the volume of the air, \(V\text{ cm}^3\), decreases.

The pressure of the air, \(P\) newtons per \(\text{cm}^2\), is inversely proportional to its volume, with \(PV=135\).

At a certain instant the air occupies \(20\text{ cm}^3\), and its volume is falling at \(8\text{ cm}^3\) per minute.

Find the rate at which the air pressure is increasing at that instant.[4]