a) $5-x=-17$
$⇔x=5-(-27)$
$⇔x=32$
b) $|7-x|.(-3)+5=2$
$⇔|7-x|.(-3)=(-3)$
$⇔|7-x|=1$
$⇔\left[ \begin{array}{l}7-x=1\\7-x=-1\end{array} \right.$
$⇔\left[ \begin{array}{l}x=6\\x=8\end{array} \right.$
c) $128-3.(x+4)=23$
$⇔3.(x+4)=128-23=105$
$⇔x+4=35$
$⇔x=31$
Chúc bạn học tốt !