Answer
$\frac{dR}{dM}=CM-M^2$
Work Step by Step
Step 1. Replace $R$ with $y$, and replace $M$ with $x$; the function can be rewritten as $y=x^2(C/2-x/3)=-x^3/3+Cx^2/2$ where $C$ is a constant.
Step 2. Find the derivative: $\frac{dy}{dx}=-x^2+Cx$
Step 3. Changing back to the original symbol, we have $\frac{dR}{dM}=-M^2+CM=CM-M^2$
