Suppose a manufacturer's revenue function is given by $\displaystyle {R}{\left({q}\right)}=-{4}{q}^{{2}}+{500}{q}$ , where $\displaystyle {R}{\left({q}\right)}$ is in dollars and $\displaystyle {q}$ is units sold.

Find the rate at which revenue is changing when $\displaystyle {q}={31}$ units.



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