Task: Question Answering
Input (English): Problem: two pipes a and b can fill a cistern in 10 and 15 minutes respectively . both fill pipes are opened together , but at the end of 3 minutes , ‘ b ’ is turned off . how much time will the cistern take to fill ? 
Options: a ) 6 min , b ) 8 min , c ) 10 min , d ) 12 min , e ) none of these
Output (English): b