Hi!
So we know she already has $9,000, and we know that she needs to earn $27,000. We also know she gets paid $4,500 per month which can be written as $4,500m (m = month). Now we have to put the equation together.
$9,000 + $4,500m = $27,000
Whatever we do to the equation, we have to do to both sides. Now let's isolate m on one side. We'll start by subtraction $9,000 from both sides.
$9,000 - $9,000 + $4,500m = $27,000 - $9,000
$4,500m = $18,000
Divide both sides by $4,500.
$4,500m/$4,500 = $18,000/$4,500
m = 4
The answer is 4 months
Hope this helps! :)
-Peredhel