a) $(\dfrac{-7}{15} - \dfrac{27}{10} ) - (\dfrac{8}{15} + \dfrac{43}{70})$
$ = \dfrac{-7}{15} - \dfrac{27}{10} - \dfrac{8}{15} - \dfrac{43}{70}$
$ = ( \dfrac{-7}{15} - \dfrac{8}{15} ) - ( \dfrac{189}{70} + \dfrac{43}{70})$
$ = -1 - \dfrac{116}{35} = \dfrac{-151}{35}$
b) $\dfrac{3}{7} + (\dfrac{-1}{5} + \dfrac{-3}{7} )$
$ = \dfrac{3}{7} - \dfrac{3}{7} + \dfrac{-1}{5}$
$ =\dfrac{-1}{5}$
c) $\dfrac{-5}{7} . \dfrac{2}{11} + \dfrac{-5}{7}. \dfrac{9}{11}$
$ = \dfrac{-5}{7}. ( \dfrac{2}{11} + \dfrac{9}{11})$
$ = \dfrac{-5}{7}. 1 = \dfrac{-5}{7}$
