\[\boxed{\text{6.16.}}\]
\[\textbf{а)}\ 7\frac{5}{11} + 5\frac{8}{11} - 2\frac{2}{11} + 2\frac{8}{11} =\]
\[= 12\frac{13}{11} - 2\frac{2}{11} + 2\frac{8}{11} =\]
\[= 10\frac{11}{11} + 2\frac{8}{11} = 12\frac{19}{11} = 13\frac{8}{11};\ \]
\[\textbf{б)}\ 9\frac{6}{15} - 5\frac{3}{5} + 4\frac{4}{15} + 2\frac{2}{5} =\]
\[= \left( 9\frac{6}{15} + 4\frac{4}{15} \right) - 5\frac{9}{15} + 2\frac{6}{15} =\]
\[= 13\frac{10}{15} - 5\frac{9}{15} + 2\frac{6}{15} =\]
\[= 8\frac{1}{15} + 2\frac{6}{15} = 10\frac{7}{15}\text{.\ \ \ }\]