Task: Question Answering
Input (English): Problem: a large tanker can be filled by two pipes a and b in 30 and 15 hours respectively . how many hours will it take to fill the tanker from empty state if a and b fill it together ? 
Options: a ) 8 hr , b ) 10 hr , c ) 12 hr , d ) 9 hr , e ) 5 hr
Output (English): b