Giúp mình với mọi người ơi

a) $\dfrac{11}{12} – \dfrac{2}{3} = \dfrac{2}{5} + x$

<-> $\dfrac{1}{4} = \dfrac{2}{5} + x$

<-> $\dfrac{1}{4} – \dfrac{2}{5} = x$

<-> $x = \dfrac{-3}{20}$.

b) 2x = 0 hoac $x-\dfrac{1}{7}= 0$ <-> $x = 0$ hoac $x = \dfrac{1}{7}$.

c) $\dfrac{1}{4}:x = \dfrac{2}{5} – \dfrac{3}{4}$

<->$\dfrac{1}{4}:x = \dfrac{-7}{20}$

<-> $x = \dfrac{1}{4}: \dfrac{-7}{20} = \dfrac{-5}{7}$.