a, $\frac{3}{7}$ - $\frac{5}{-6}$ + $\frac{3}{-7}$ = $\frac{3}{7}$ + $\frac{3}{-7}$ - $\frac{5}{-6}$
= - $\frac{5}{-6}$
b, ( $\frac{-1}{6}$ + $\frac{5}{12}$) + $\frac{7}{-12}$ = $\frac{-1}{3}$
c, $ \frac{2}{-3}^{2}$ + +$\frac{-3}{4}$ = $\frac{-13}{18}$
d , $\frac{3}{5}$ - $\frac{2}{5}$ x $\frac{10}{12}$ = $\frac{4}{15}$