Question

A dose, D, of a drug causes a temperature change, T, in apatient. For C a positive constant, t is given by T=((C/2)-(D/3))D^3.

(a) What is the rate of change of temperature change with respect to dose.
(b) For what dose does the temperature change increase as the dose increases.

For part a I got CD^2-D^3=0
For part b I got c^2/4

Any help would be greatly appreciated.