Task: Question Answering
Input (English): Problem: three pipes a , b and c can fill a tank from empty to full in 30 minutes , 20 minutes and 10 minutes respectively . when the tank is empty , all the three pipes are opened . a , b and c discharge chemical solutions p , q and r respectively . what is the proportion of solution r in the liquid in the tank after 3 minutes ? 
Options: a ) 6 / 15 , b ) 6 / 11 , c ) 6 / 14 , d ) 6 / 12 , e ) 6 / 13
Output (English): b