Task: Question Answering
Input (English): Problem: pipe a can fill a tank in 60 min . there is a second pipe in the bottom of the cistern to empty it . if all the two pipes are simultaneously opened , then the cistern is full in 180 min . in how much time , the second pipe alone can empty the cistern ? 
Options: a ) 60 min , b ) 45 min , c ) 90 min , d ) 70 min , e ) 30 min
Output (English): b