Task: Question Answering
Input (English): Problem: pipes a and b can fill a tank in 6 and 4 hours . pipe c can empty it in 12 hours . if all pipes are opened together , then the tank will be filled in ? 
Options: a ) 3 hr , b ) 2 hr , c ) 1 hr , d ) 9 / 7 hr , e ) 5 / 3 hr
Output (English): a