6 8.17--15- 17 17 9

8. $$17\frac{6}{17}-15\frac{9}{17} = (17-15) + (\frac{6}{17} - \frac{9}{17}) = 2 - \frac{3}{17} = 1 + 1 - \frac{3}{17} = 1 + \frac{17}{17} - \frac{3}{17} = 1\frac{14}{17}$$.

Ответ: $$1\frac{14}{17}$$