б) 4:2\frac{2}{7} = \frac{5}{8}:x.

Решим уравнение:

$$4:2\frac{2}{7} = \frac{5}{8}:x$$

$$4:\frac{16}{7} = \frac{5}{8}:x$$

$$ \frac{4 \cdot 7}{16} = \frac{5}{8}:x$$

$$\frac{7}{4} = \frac{5}{8}:x$$

$$x = \frac{5}{8}:\frac{7}{4}$$

$$x = \frac{5}{8} \cdot \frac{4}{7}$$

$$x = \frac{5}{2} \cdot \frac{1}{7}$$

$$x = \frac{5}{14}$$

Ответ:$$\frac{5}{14}$$