\[\boxed{\text{6.151.}}\]
\[\textbf{а)}\ 4\frac{9}{13} - 2\frac{4}{13} = 2\frac{5}{13}\]
\[\textbf{б)}\ 1 + \frac{9}{19} = 1\frac{9}{19}\text{\ \ }\]
\[\textbf{в)}\ \frac{3}{7} \cdot 2 = \frac{6}{7}\]
\[\textbf{г)}\ \frac{8}{11}\ :4 = \frac{8}{11} \cdot \frac{1}{4} = \frac{2}{11}\]