The table shows the amount earned for washing cars. how much is earned for washing 25 cars? 3 cars=$13.50, 6 cars=$27, 9 cars=$40.50, and 12 cars=$54

You need to find out how much it costs to wash one car, so:

3×=13.50
Divide both sides by 3.
x=4.5 per car. 
Now multiply 4.5 by 25 which should give you $112.50