( $\frac{3x}{7}$ + 1 ) : (-4) = $\frac{-1}{28}$
$\frac{3x}{7}$ + 1 = $\frac{-1}{28}$ . (-4)
$\frac{3x}{7}$ + 1 = $\frac{1}{7}$
$\frac{3x}{7}$ = $\frac{1}{7}$ - 1
$\frac{3x}{7}$ = $\frac{1-7}{7}$
$\frac{3x}{7}$ = $\frac{-6}{7}$
⇒ 3x = -6
⇒ x = -6 : 3
⇒ x = -2
Chúc bạn học tốt ^^