The sixth grade runs a bake sale for 55 hours and makes $170$170. the seventh grade sets up a dunking booth for 44 hours and makes $112$112. the eighth grade has a car wash and makes $192$192 in 66 hours. which class has the highest rate for raising money?

The answer is the sixth grade class.

In order to find the answer, you have to divide each grade's total by the number of hours it took them to make that money, which will give you the amount each class makes per hour. 

$170 / 55 = $3.09
$112 / 44 = $2.54
$192 / 66 = $2.91