Another Related Rates problem

A certain quantity of gas occupies a volume of 20cm^3 at a pressure of 1 atmosphere. The gas expans wihtout the addition of heat, ,so, for some constant *k*, its pressure, *P*, and volume, *V*, satisfy the relation

(a) Find the rate of change of pressure with volume. Give units.

(b) The volume is increasing at 2 cm^3/min when the volume is 30 cm^3. At that moment, is the pressure increasing or decreasing? How fast? Give units.

The thing that confuses me about this problem is that it says the gas occupies a volume of 20cm^3 at a pressure of 1 atmosphere. I didn't use this information when I worked the problem. Could this information not be needed, or did I screw up somewhere?

Anyways, here is my work:

(a)

atm/cm^3

(b)

atm/min

decreasing at approximately 0.000798 atm/min