2/3 * 6/7 = ?

$$\frac{2}{3} \cdot \frac{6}{7} = \frac{2 \cdot 6}{3 \cdot 7} = \frac{12}{21}$$
Сократим дробь на 3:
$$\frac{12}{21} = \frac{12:3}{21:3} = \frac{4}{7}$$

Ответ: 4/7