8. 17 -15

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

Ответ: $$1 \frac{14}{17}$$