Answer
$x\geq\frac{c-b}{x}$ or $x\leq\frac{-c-b}{x}$.
Work Step by Step
$|ax+b|\geq c$ implies $ax+b\geq c\\ax\geq c-b\\x\geq\frac{c-b}{x}$ or $ax+b\leq -c\\ax\leq -c-b\\x\leq\frac{-c-b}{x}$.
Thus $x\geq\frac{c-b}{a}$ or $x\leq\frac{-c-b}{a}$.