Task: Question Answering
Input (English): Problem: an empty fuel tank with a capacity of 200 gallons was filled partially with fuel a and then to capacity with fuel b . fuel a contains 12 % ethanol by volume and fuel b contains 16 % ethanol by volume . if the full fuel tank contains 20 gallons of ethanol , how many gallons of fuel a were added ? 
Options: a ) 300 , b ) 150 , c ) 100 , d ) 80 , e ) 50
Output (English): a