2) $$ \frac{2m^{-3}}{5n^{-2}} \cdot \frac{15n}{m^{-5}} = \frac{2}{5} \cdot \frac{15}{1} \cdot \frac{m^{-3}}{m^{-5}} \cdot \frac{n}{n^{-2}} = 6 m^{-3-(-5)} n^{1-(-2)} = 6 m^{2} n^{3} $$.
4) $$ \frac{3m^{4}}{2n^{3}} : \left( \frac{3^{-1}m^{-2}}{2n^{-4}} \right)^{2} = \frac{3m^{4}}{2n^{3}} : \frac{(3^{-1})^2 (m^{-2})^2}{(2)^2 (n^{-4})^2} = \frac{3m^{4}}{2n^{3}} : \frac{3^{-2} m^{-4}}{4n^{-8}} = \frac{3}{2} \cdot \frac{4}{3^{-2}} \cdot \frac{m^{4}}{m^{-4}} \cdot \frac{n^{-8}}{n^{3}} = \frac{3 \cdot 4}{3^{-2} \cdot 2} \cdot m^{4-(-4)} n^{-8-3} = \frac{12 \cdot 3^{2}}{2} m^{8} n^{-11} = \frac{12 \cdot 9}{2} m^{8} n^{-11} = 54 \cdot \frac{m^{8}}{n^{11}} = \frac{54m^{8}}{n^{11}} $$.
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