Cứu với ạ cứu tui ko

a) $\frac{3}{7}$.$\frac{9}{26}$-$\frac{1}{14}$.$\frac{1}{13}$-$\frac{1}{7}$

=$\frac{27}{182}$-$\frac{1}{182}$- $\frac{1}{7}$

= $\frac{1}{7}$- $\frac{1}{7}$

= 0

b) $\frac{-5}{6}$. $\frac{4}{19}$+ $\frac{-7}{12}$. $\frac{4}{19}$- $\frac{40}{57}$

=[ $\frac{-5}{6}$+$\frac{-7}{12}$]. $\frac{4}{19}$- $\frac{40}{57}$

=$\frac{-17}{12}$. $\frac{4}{19}$-$\frac{40}{57}$

= $\frac{-17}{57}$- $\frac{40}{57}$

=-1