c.
$\frac{3}{7}$:(x+20)= $\frac{6}{42}$
x+20=$\frac{3}{7}$: $\frac{6}{42}$
x+20=$\frac{3}{7}$ x $\frac{42}{6}$
x+20=3
x=-17
Vậy x=-17
d.
(4,5-2x)-$\frac{3}{4}$=1$\frac{1}{3}$
$\frac{9}{2}$-2x=$\frac{4}{3}$+ $\frac{3}{4}$
$\frac{9}{2}$-2x=$\frac{25}{12}$
-2x=$\frac{25}{12}$-$\frac{54}{12}$
-2x=$\frac{-29}{12}$
x=$\frac{-29}{12}$ x $\frac{-1}{2}$
x=$\frac{29}{24}$
Vậy x=$\frac{29}{24}$
