6) \(\frac{21}{5}\cdot\frac{3}{7}\)

Сократим 21 и 7:

\(\frac{21}{5}\cdot\frac{3}{7}=\frac{3}{5}\cdot3=\frac{9}{5}=1\frac{4}{5}\).

Ответ: \(1\frac{4}{5}\)