\[\left( \frac{x^{8}}{y^{- 5}} \right)^{- 4} \cdot \left( \frac{x^{- 4}}{y^{8}} \right)^{- 10} =\]
\[= \frac{x^{- 32}}{y^{20}} \cdot \frac{x^{40}}{y^{- 80}} = \frac{x^{8}}{y^{- 60}} = x^{8}y^{60}.\]