Answer
$\dfrac{2n^{7-3}}{3}$
Work Step by Step
Using $\dfrac{a^x}{a^y}=a^{x-y}$, then the expression, $
\dfrac{10n^7}{15n^3}
$, simplifies to
\begin{array}{l}\require{cancel}
\dfrac{\cancel{5}\cdot2n^{7-3}}{\cancel{5}\cdot3}
\\\\=
\dfrac{2n^{7-3}}{3}
.\end{array}