Answer
$(-\infty,-3]$
Work Step by Step
$-3x\geq9$
Solve for x by multiplying each side by -3. When multiplying by a negative number you must reverse the inequality sign
$-3x\div-3\leq9\div-3$
$x\leq-3$
This is expressed in interval notation as
$(-\infty,-3]$
where ] indicates that -3 is included in the solution set for x.