Use the following information to answer questions 18-20.

The gas tank in Mark's car has a fuel capacity of 18 gallons of gasoline. The car averages 24 miles per gallon when driven at highway speeds and 21 miles per gallon when driven at city speeds. Approximately 90% of the 30, 000 miles Mark drives each year are at highway speeds. The average price of Mark's gasoline is $1.699 per gallon.