Tính: -5/7.2/7 + -5/.9/11 + 1(5/7)

$$\begin{gathered} a, \frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+1\frac{5}{7} \\ b, 11\frac{3}{13} - ( 2\frac{4}{7} + 5\frac{3}{13 } ) \end{gathered}$$

 tính