Bạn tham khảo :
$a,$
$\dfrac{-5}{12} - 0,75 = \dfrac{-5}{12} - \dfrac{3}{4} = \dfrac{-5}{12} - \dfrac{9}{12} = \dfrac{-14}{12} = \dfrac{-7}{6}$
$b,$
$3,5 - \dfrac{-2}{7} = \dfrac{35}{10} + \dfrac{2}{7} = \dfrac{245}{70} + \dfrac{20}{70} = \dfrac{265}{70}= \dfrac{53}{14}$