Answer:
[tex]\large\boxed{\left\{\begin{array}{ccc}x\leq\dfrac{20}{a}&\text{for}\ a>0\\\\x\geq\dfrac{20}{a}&\text{for}\ a<0\end{array}\right }[/tex]
Step-by-step explanation:
[tex]ax-8\leq12\qquad\text{add 8 to both sides}\\\\ax-8+8\leq12+8\\\\ax\leq20\qquad\text{divide both sides by}\ a\neq0\\\\(1)\ \text{if}\ a>0,\ \text{then:}\\\\x\leq\dfrac{20}{a}\\\\(2)\ \text{if}\ a<0,\ \text{then you must flip the sign of inequality:}\\\\x\geq\dfrac{20}{a}[/tex]
