Jon is paid $20 to mow his neighbor's yard. It takes three hours to mow and $2 worth of gasoline. How much does Jon earn per hour?

Jon earns 6 dollars per hour.

We know this because, if he gets paid $20 and buys $2 worth of gasoline, his profit is $18.

Then, we divide 18 by the number of hours he worked, 3, and thus, Jon earns $6/hr.