Answer
$-375$
Work Step by Step
Using $x^{-a}=\dfrac{1}{x^a}$ and $\dfrac{1}{x^{-a}}=x^a,$ the given expression, $
\dfrac{3}{(-5)^{-3}}
,$ simplifies to
\begin{array}{l}\require{cancel}
3\cdot(-5)^3
\\\\=
3\cdot(-125)
\\\\=
-375
.\end{array}