Task: Question Answering
Input (English): Problem: a certain car can travel 40 minutes on a gallon of gasoline at 60 miles per hour. if the car had started with a full tank and had 6 gallons of gasoline left in its tank at the end, then what percent of the tank was used to travel 80 miles at 60 mph ?
Options: a. 15 %, b. 20 %, c. 25 %, d. 30 %, e. 40 %
Output (English): c