Task: Question Answering
Input (English): Problem: a & b can separately do a piece of work in 20 & 15 days . they worked together for 6 days , after which b was replaced by c . the work was finished in next 5 days . the no . of days in which c alone could do the work is 
Options: a ) 10 days , b ) 20 days , c ) 30 days , d ) 40 days , e ) 50 days
Output (English): e