Answer
$$ \text{net profit margin} = \frac{.48x^3+2.06x^2+141x+9.72}{1011x-288}$$
Work Step by Step
We know that net profit margin is given by the net profit over the revenue. This means:
$$ \text{net profit margin} = \frac{P(x)}{R(x)}$$
Since both of these polynomials are given in the problem, we find:
$$ \text{net profit margin} = \frac{.48x^3+2.06x^2+141x+9.72}{1011x-288}$$
