G9.3 If the lines $2 y+x+3=0$ and $3 y+c x+2=0$ are perpendicular, find the value of $c$.
$\begin{array}{l}\text { Product of slopes }=-1 \\ -\frac{1}{2} \times\left(-\frac{c}{3}\right)=-1 \\ c=-6\end{array}$