Task: Question Answering
Input (English): Problem: a cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 7 hours . if both the taps are opened simultaneously , then after how much time will the cistern get filled ? 
Options: a ) 9.5 , b ) 9.4 , c ) 9.3 , d ) 9.2 , e ) 9.1
Output (English): c