I2.4 If $\sin A=\frac{p}{5}$ and $\frac{\cos A}{\tan A}=\frac{q}{15}$, find $q$.
$\begin{array}{l}\sin A=\frac{3}{5} \\ \frac{\cos A}{\tan A}=\frac{q}{15} \\ \frac{\cos ^{2} A}{\sin A}=\frac{q}{15} \\ \frac{1-\sin ^{2} A}{\sin A}=\frac{1-\left(\frac{3}{5}\right)^{2}}{\frac{3}{5}}=\frac{16}{15}=\frac{q}{15} \\ q=16\end{array}$