Suppose a product's revenue function is given by $\displaystyle {R}{\left({q}\right)}=-{7}{q}^{{2}}+{400}{q}$ , where $\displaystyle {R}{\left({q}\right)}$ is in dollars and $\displaystyle {q}$ is units sold.

Find a numeric value for the marginal revenue at $\displaystyle {40}$ units, and record your result in the box below.

Answer: $\displaystyle {M}{R}{\left({40}\right)}=$ $\displaystyle \${p}{e}{r}{u}{n}{i}{t}$