\[\boxed{\text{6.240.}}\]
\[\textbf{а)}\ \frac{3}{17} + \frac{6}{17} < \frac{2}{17} + \frac{8}{17}\]
\[\text{\ \ \ \ \ }\frac{9}{17} < \frac{10}{17}\ \]
\[\textbf{б)}\ \frac{7}{19} - \frac{3}{19} < \frac{9}{16} - \frac{5}{16}\ \]
\[\text{\ \ \ \ \ }\frac{4}{19} < \frac{4}{16}\]