\[\boxed{\text{П.13.}}\]
\[\textbf{а)}\ 7\frac{5}{6} - \left( 4\frac{4}{9} - 2\frac{4}{9} \right) + 6\frac{1}{6} =\]
\[= \left( 7\frac{5}{6} + 6\frac{1}{6} \right) - \left( 4\frac{4}{9} - 2\frac{4}{9} \right) =\]
\[= 14 - 2 = 12\]
\[= 7\frac{2}{16} - 1 = 6\frac{2}{16}\text{\ \ }\]