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