Three men do as much work as 4 boys do and the 4 boys can together complete work in 21 days. In how many days will 9 men and 2 boys complete the same work?

A and B together can complete a certain work in 20 days whereas B and C together can complete it in 24 days. If A is twice as good a workman as C, then in what time will B alone do 40% of the same work?