$$-\frac{7}{8} - (-\frac{16}{49}) = -\frac{7}{8} + \frac{16}{49} = \frac{-7 \cdot 49 + 16 \cdot 8}{8 \cdot 49} = \frac{-343 + 128}{392} = \frac{-215}{392}$$
Ответ: -215/392