Laske.

a) [[$ \dfrac{1}{2} - \left(- \dfrac{1}{4} \right) $]] =

b) [[$ -\dfrac{4}{5} + \left( - \dfrac{5}{4} \right) $]] =

c) [[$ \dfrac{9}{10} - \left( + \dfrac{3}{4} \right) $]] =

d) [[$ - \dfrac{6}{8} - \dfrac{1}{16} $]] =