Q$6(3$ points$)$

This question is based on Section $4\mathrm{.}7.$

Suppose Madame Dory is selling pizzas at her pizzeria. If her revenue is given by the function $R(x)=15x$ and her costs are given by the function $C(x)=60+3x+\frac{1}{2}{x}^2,$ how many pizzas must this stunning Boston Terrier sell in order to maximize her profit?