Answer
$\color{blue}{\huge \mathbf{ \frac{mn}{r^2}}}$
Work Step by Step
$\large \frac{m}{r}*\frac{n}{r} \ne \large \frac{mn}{r}$
Lets work this through:
$\large \frac{m}{r}*\frac{n}{r} = \large \frac{(m)(n)} {(r)(r)} $
$\color{blue}{\large \mathbf{ \frac{mn}{r^2}}}$
