A man, a woman and a boy can complete a job in 3, 5 and 15 days respectively. When working together, how many boys must assist one man and one woman to complete the work in 14 of a day?

If P and Q together can complete a piece of work in 15 days and P alone can do it in 45 days, in how many days can Q alone complete that work?

A can lay a railway track between two stations in 16 days and B can do the same job in 12 days. With the help of C, they finished the job in 4 days. In how many days can C alone do the job?