Mọi người giúp mình với !!!!!!

$\text{a)$\dfrac{x}{15}$ + $\dfrac{-4}{15}$ = $\dfrac{8}{15}$ }$$\\$ $\text{=> $\dfrac{x}{15}$ = $\dfrac{8}{15}$ - $\dfrac{-4}{15}$ }$$\\$ $\text{=> $\dfrac{x}{15}$ = $\dfrac{8 - (-4)}{15}$ }$$\\$ $\text{=> $\dfrac{x}{15}$ = $\dfrac{8 + 4}{15}$ }$$\\$ $\text{=> $\dfrac{x}{15}$ = $\dfrac{12}{15}$ }$$\\$ $\text{=> x = 12}$$\\$ $\text{Vậy x = 12}$$\\$ $\text{b) $\dfrac{-7}{16}$ + $\dfrac{x}{16}$ = $\dfrac{7}{8}$}$$\\$ $\text{=>$\dfrac{-7}{16}$ + $\dfrac{x}{16}$ = $\dfrac{14}{16}$}$$\\$ $\text{=>$\dfrac{x}{16}$ = $\dfrac{14}{16}$ + $\dfrac{7}{16}$ }$$\\$ $\text{=>$\dfrac{x}{16}$ = $\dfrac{14 + 7}{16}$}$$\\$ $\text{=>$\dfrac{x}{16}$ = $\dfrac{21}{16}$}$$\\$ $\text{=> x = 21}$$\\$ $\text{Vậy x = 21}$$\\$ $\text{c)x - $\dfrac{-18}{54}$ = $\dfrac{7}{9}$ }$$\\$ $\text{=> x + $\dfrac{3}{9}$ = $\dfrac{7}{9}$}$$\\$ $\text{=> x = $\dfrac{7}{9}$ - $\dfrac{3}{9}$}$$\\$ $\text{=> x = $\dfrac{7-3}{9}$}$$\\$ $\text{=> x = $\dfrac{4}{9}$}$$\\$ $\text{Vậy x = $\dfrac{4}{9}$}$$\\$ $\text{d)$\dfrac{-14}{42}$ - x = $\dfrac{-3}{7}$ }$$\\$ $\text{=> $\dfrac{-1}{3}$ - x = $\dfrac{-3}{7}$ }$$\\$ $\text{=> x = $\dfrac{-1}{3}$ -$\dfrac{-3}{7}$ }$$\\$ $\text{=> x = $\dfrac{-7}{21}$ -$\dfrac{-9}{21}$ }$$\\$ $\text{=> x = $\dfrac{-7+9}{21}$}$$\\$ $\text{=> x = $\dfrac{2}{21}$}$$\\$ $\text{Vậy x = $\dfrac{2}{21}$}$$\\$