8. $$5 \sqrt[6]{6^{10} \cdot (\frac{1}{6})^{15}} = 5 \sqrt[6]{6^{10-15}} = 5 \sqrt[6]{6^{-5}} = 5 \sqrt[6]{\frac{1}{6^5}} = \frac{5}{\sqrt[6]{6^5}} = \frac{5}{\sqrt[6]{7776}}$$.
Ответ: 5/$$\sqrt[6]{7776}$$