#### Answer

$\text{undefined}$

#### Work Step by Step

Substituting $p=-4$ and $r=16,$ the given expression, $
\dfrac{\sqrt{r}}{8p+2r}
,$ evaluates to
\begin{array}{l}\require{cancel}
\dfrac{\sqrt{16}}{8(-4)+2(16)}
\\\\=
\dfrac{4}{-32+32}
\\\\=
\dfrac{4}{0}
\\\\=
\text{undefined}
.\end{array}