3. Выполни действия: \(\frac{7}{8}\cdot\frac{4}{21}+\frac{5}{9}:\frac{10}{27}-\left(\frac{1}{3}\right)^2\).

\[\frac{7}{8}\cdot\frac{4}{21}+\frac{5}{9}:\frac{10}{27}-\left(\frac{1}{3}\right)^2=\frac{1}{6}+\frac{5}{9}\cdot\frac{27}{10}-\frac{1}{9}\]

\[=\frac{1}{6}+\frac{3}{2}-\frac{1}{9}=\frac{3}{18}+\frac{27}{18}-\frac{2}{18}=\frac{28}{18}=\frac{14}{9}=1\frac{5}{9}.\]

Ответ: \(1\frac{5}{9}\).