# A and B can separately finish a piece of work in 20 days and 15 days respectively

A and B can separately finish a piece of work in 20 days and 15 days respectively. They worked together for 6 days, after which B was replaced by C. If the work was finished in next 4 days, then the number of days in which C alone could do the work is

(a) 50 days

(b) 30 days

(c) 40 days

(d) 60 days