Task: Question Answering
Input (English): Problem: pipe a fills a tank in 56 minutes . pipe b can fill the same tank 7 times as fast as pipe a . if both the pipes are kept open when the tank is empty , how many minutes will it take to fill the tank ? 
Options: a ) 4 , b ) 5 , c ) 6 , d ) 7 , e ) 8
Output (English): d