Task: Question Answering
Input (English): Problem: a , b , c can do a piece of work in 11 days , 20 days and 55 days respectively , working alone . how soon can the work be done if a is assisted by b and c on alternate days ? 
Options: a ) 2 , b ) 4 , c ) 8 , d ) 10 , e ) 12
Output (English): c