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

Сократим 21 и 6 на 3: \(\frac{21}{6}=\frac{7}{2}\).

\(\frac{21}{5}\cdot\frac{7}{6}=\frac{49}{10}=4\frac{9}{10}\).

Ответ: \(\frac{49}{10}=4\frac{9}{10}\)