When the volume of a gas changes very rapidly, anapproximate relation is that the pressure (P) varies inversely as the3/2 power of the volume. If (P) is 300kPa when V=100cm^3, find the derivative of P with respect to V. Evaluate this derivative for V=100cm^3.

This is a word problem in my homework that I am getting nowhere on. I do know from the back of the book thatthe answer is -450,000/(V^(5/2)) <--the derivative

and the evaluated derivative is -4.50kPa/cm^3

I, however, have no clue how to get these answers.