Answer
(a) $x = 2.5$ is the only critical number.
(b) The maximum revenue is $\$375$, which occurs when the price is $\$2.50$.
Work Step by Step
(a). $R'(x) = −120x + 300$, which is zero when $x = 2.5$. This is the only critical number.
b. The maximum must occur at either an endpoint or a critical point. Note that $R(0) = 0$, $R(2.5) = 375$, and $R(5) = 0$, so the maximum revenue is $\$375$, which occurs when the price is $\$2.50$.
