\[\left( \frac{2^{\backslash 3}}{7} - \frac{2^{\backslash 7}}{3} \right)\ :1\frac{1}{7} + 0,9 \cdot \left( - \frac{5}{9} \right) - 0,6\ :( - 1,2) =\]
\[= \left( \frac{6}{21} - \frac{14}{21} \right)\ :\frac{8}{7} - \frac{9}{10} \cdot \frac{5}{9} + 6\ :12 =\]
\[= - \frac{8}{21} \cdot \frac{7}{8} - \frac{1}{2} + \frac{6}{12} =\]
\[= - \frac{1}{3} - \frac{1}{2} + \frac{1}{2} = - \frac{1}{3}.\]