Task: Question Answering
Input (English): Problem: two pipes a and b can separately fill a cistern in 60 min and 75 min respectively . there is a third pipe in the bottom of the cistern to empty it . if all the 3 pipes are simultaneously opened , then the cistern is full in 50 min . in how much time , the third pipe alone can empty the cistern ? 
Options: a ) 197 min , b ) 100 min , c ) 177 min , d ) 176 min , e ) 186 min
Output (English): b