Task: Question Answering
Input (English): Problem: two pipes can fill a tank in 20 minutes and 15 minutes . an outlet pipe can empty the tank in 10 minutes . if all the pipes are opened when the tank is empty , then how many minutes will it take to fill the tank ? 
Options: a ) 36 , b ) 42 , c ) 48 , d ) 54 , e ) 60
Output (English): e