Task: Question Answering
Input (English): Problem: pipe a can fill a tank in 3 hours . due to a leak at the bottom , it takes 9 hours for the pipe a to fill the tank . in what time can the leak alone empty the full tank ? 
Options: a ) 4.5 , b ) 17 , c ) 18 , d ) 19 , e ) 12
Output (English): a