Task: Question Answering
Input (English): Problem: pipe p can fill a tank in 8 hours , pipe q in 12 hours and pipe r in 20 hours . if all the pipes are open , in how many hours will the tank be filled ? 
Options: a ) 2 hours , b ) 2.4 hours , c ) 3.8 hours , d ) 3.5 hours , e ) 4.5 hours
Output (English): c