7 (8³)⁻⁷/8⁻²³;

7. $$\frac{(8^3)^{-7}}{8^{-23}} = \frac{8^{-21}}{8^{-23}} = 8^{-21-(-23)} = 8^{-21+23} = 8^2 = 64 $$.

Ответ: 64