Task: Question Answering
Input (English): Problem: pipe a fills a tank in 42 minutes . pipe b can fill the same tank 6 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 ) 3 , b ) 4 , c ) 5 , d ) 6 , e ) 7
Output (English): d