5 15. 8--7- 16

$$8\frac{5}{16} - 7\frac{9}{16} = (8-7) + (\frac{5}{16} - \frac{9}{16}) = 1 - \frac{4}{16} = 1 - \frac{1}{4} = \frac{4}{4} - \frac{1}{4} = \frac{3}{4}$$

Ответ: $$\frac{3}{4}$$