Maximizing Profit. In business, profit is the difference between revenue and cost; that is,
$$
\begin{array}{l}
\text { Total profit }=\text { Total revenue }-\text { Total cost, } \\
P(x)=R(x)-C(x)
\end{array}
$$
where $x$ is the number of units sold. Find the maximum profit and the number of units that must be sold in order to yield the maximum profit for each of the following.
$$
R(x)=5 x, C(x)=0.001 x^{2}+1.2 x+60
$$