Answer
$\dfrac{25}{z^4}$
Work Step by Step
Using the laws of exponents, the given expression, $
\left( \dfrac{5z^{-3}}{z^{-1}} \right)\dfrac{5}{z^2}
,$ simplifies to
\begin{array}{l}\require{cancel}
\dfrac{5z^{-3}\cdot5}{z^{-1}\cdot z^2}
\\\\=
\dfrac{5^{1+1}z^{-3}}{z^{-1+2}}
\\\\=
\dfrac{5^{2}z^{-3}}{z^{1}}
\\\\=
5^{2}z^{-3-1}
\\\\=
25z^{-4}
\\\\=
\dfrac{25}{z^4}
.\end{array}
