25. Вычислите: \(6{,}8-5\frac{5}{9}\).

\[6{,}8=6\frac{4}{5},\quad 6\frac{4}{5}-5\frac{5}{9}=1+\frac45-\frac59=1+\frac{36-25}{45}=1\frac{11}{45}.\]

Ответ: \(1\frac{11}{45}\).