Task: Question Answering
Input (English): Problem: pipe a fills a swimming pool in 4 hours . pipe b empties the pool in 6 hours . if pipe a was opened at 7 : 00 am and pipe b at 8 : 00 am , at what time will the pool be full ? 
Options: a ) 16 : 00 , b ) 18 : 00 , c ) 19 : 00 , d ) 20 : 00 , e ) 17 : 00
Output (English): e