\[\boxed{\mathbf{877\ (877)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\textbf{а)}\ \]
\[- \frac{5}{7};\ \ - \frac{4}{7};\ - \frac{3}{7}.\]
\[\textbf{б)}\ \]
\[- \frac{12}{7};\ \ - \frac{11}{7};\ - \frac{10}{7};\ - \frac{9}{7}.\]