To solve each problem, refer to the formulas for compound interest.
$$A=P\left(1+\frac{r}{n}\right)^{m} \text { and } A=P e^{n t}$$
At what interest rate, to the nearest hundredth of a percent, will $\$ 16,000$ grow to $\$ 20,000$ if invested for 7.25 yr and interest is compounded quarterly?