Task: Question Answering
Input (English): Problem: it will take 18 days for cameron to complete a certain task alone . he worked for 9 days before she was joined by sandra . both of them completed the remaining task in 3 and half days . how many days will it take both of them to complete the entire job ? 
Options: a ) 6 , b ) 7 , c ) 5 , d ) 8 , e ) 9
Output (English): b