4. Twelve men can complete a work in 8 days. Three days after they stated the work, 3 more men joined them. In how many days will all of them together complete the remaining work?

5. A can complete a job in 9 days, B in 10 days and C in 15 days. B and C start the work and are forced to leave after 2 days. The time taken to complete the remaining work is:

6. A can do a piece of work in 20 days which B can do in 12 days. B worked at it for 9 days. A can finish the remaining work in: