6(15):2:6-2

Решим пример:

$$\begin{aligned}
\left(15\frac{1}{3} - 8\frac{5}{18}\right) : 2\frac{6}{7} - 2\frac{5}{8} = \left(\frac{46}{3} - \frac{149}{18}\right) : \frac{20}{7} - \frac{21}{8} = \left(\frac{46 \cdot 6 - 149}{18}\right) : \frac{20}{7} - \frac{21}{8} = \left(\frac{276 - 149}{18}\right) : \frac{20}{7} - \frac{21}{8} = \frac{127}{18} : \frac{20}{7} - \frac{21}{8} = \frac{127}{18} \cdot \frac{7}{20} - \frac{21}{8} = \frac{889}{360} - \frac{945}{360} = -\frac{56}{360} = -\frac{7}{45}
\end{aligned}$$

Ответ: $$\frac{-7}{45}$$