3m2 n-5 * m-2 n-3
\(3\cdot m^2\cdot n^{-5}\cdot m^{-2}\cdot n^{-3} \\~\\ =3\cdot m^2 \cdot m^{-2} \cdot n^{-5}\cdot n^{-3} \\~\\ =3\cdot m^{2+-2}\cdot n^{-5 + -3} \\~\\ =3\cdot m^0\cdot n^{-8} \\~\\ =3\cdot n^{-8}\)
And
\(3 \times n^{-8}\\ =3 \times \frac{1}{n^{+8}}\\ =\frac{3}{n^8}\)