18. Вычислите: \(\frac{11}{8}\cdot\frac{15}{16}:\frac{25}{28}\).

\[\frac{11}{8}\cdot\frac{15}{16}:\frac{25}{28}=\frac{11}{8}\cdot\frac{15}{16}\cdot\frac{28}{25}=\frac{231}{160}.\]

Ответ: \(\frac{231}{160}\).