6) 7/8 * (-4/21)

$$\frac{7}{8} \cdot (-\frac{4}{21}) = -\frac{7 \cdot 4}{8 \cdot 21} = -\frac{1 \cdot 1}{2 \cdot 3} = -\frac{1}{6}$$

Ответ: -1/6