\[\boxed{\text{6.241.}}\]
\[\textbf{а)}\ \frac{3}{17} + \frac{6}{17} < \frac{2}{17} + \frac{8}{17}\]
\[\text{\ \ \ \ \ }\frac{9}{17} < \frac{10}{17}\ \]
\[\textbf{б)}\ \frac{7}{19} - \frac{3}{19} < \frac{9}{16} - \frac{5}{16}\ \]
\[\text{\ \ \ \ \ }\frac{4}{19} < \frac{4}{16}\]
\[\textbf{в)}\ \frac{7}{10} \cdot \frac{5}{14} = \frac{1}{4};\]
\[\frac{3}{8}\ :\frac{9}{16} = \frac{3}{8} \cdot \frac{16}{9} = \frac{2}{3};\]
\[\frac{1}{4} = \frac{3}{12} < \frac{2}{3} = \frac{8}{12}.\]