Task: Question Answering
Input (English): Problem: a 2000 liter tank , half - full of water is being filled from a pipe with a flow rate of 1 kiloliter every 2 minutes . at the same time , the tank is losing water from two drains at a rate of 1 kiloliter every 4 minutes and every 6 minutes . how many minutes does it take to fill the tank completely ? 
Options: a ) 8 , b ) 12 , c ) 18 , d ) 24 , e ) 48
Output (English): b