Task: Question Answering
Input (English): Problem: a can do a piece of work in 40 days ; b can do the same in 30 days . a started alone but left the work after 10 days , then b worked at it for 10 days . c finished the remaining work in 10 days . c alone can do the whole work in ? 
Options: a ) 24 days , b ) 65 days , c ) 86 days , d ) 45 days , e ) 17 days
Output (English): a