Task: Question Answering
Input (English): Problem: a tank holds x gallons of a saltwater solution that is 20 % salt by volume . one fourth of the water is evaporated , leaving all of the salt . when 6 gallons of water and 12 gallons of salt are added , the resulting mixture is 33 1 / 3 % salt by volume . what is the value of x ? 
Options: a ) 37.5 , b ) 75 , c ) 100 , d ) 150 , e ) 90
Output (English): e