\[\left( \frac{3}{5}a^{- 8}b^{- 7} \right)^{- 3} \cdot \left( - 5a^{6}b^{12} \right)^{- 2} =\]
\[= \left( \frac{5}{3} \right)^{3}a^{24}b^{21} \cdot \left( \frac{1}{5} \right)^{2}a^{- 12}b^{- 24} =\]
\[= \frac{5^{3}}{27 \cdot 5^{2}}a^{12}b^{- 3} = \frac{5a^{12}}{27b^{3}}\]