One person buys a compact sedan that costs $21,000 and gets 25 miles per gallon. Another person pays $25,000 for the hybrid version of the same compact sedan, which gets 50 miles per gallon. Each owner drives 12,000 miles per year and plans on keeping the vehicle for 10 years.
A gallon of gas emits 20 pounds of CO, when burned in an internal combustion engine. The average cost of a gallon of gas over the 10-year ownership period is $3.00.

Calculate how many gallons of gas each vehicle uses per year.