6. \(\frac{7}{9}-\left(\frac{1}{18}+\frac{7}{18}\right)\)

\(\frac{1}{18}+\frac{7}{18}=\frac{8}{18}=\frac{4}{9}\).

\(\frac{7}{9}-\frac{4}{9}=\frac{3}{9}=\frac{1}{3}\).

Ответ: \(\frac{1}{3}\)