If Dale has a constant rate that means no matter how many hours, every hour he mows he will mow 18 miles. He mowed for 6 hours, so all you have to do is multiply 6*18, and your answer is 108 miles.
The reason is because it is not just 6 it is - 6 so when there are two negative numbers they don't subtract they add if it was 6n then it was to be subtracted
