Laske.

a) [[$ \dfrac{3}{a} + \dfrac{4}{2a} $]] =

b) [[$ \dfrac{1}{5x} + \dfrac{1}{10x} $]] =

c) [[$ \dfrac{5}{6b} - \dfrac{2}{3b} $]] =

d) [[$ \dfrac{4}{3y} - \dfrac{1}{2y} $]] =