A alone can do a piece of work in 14 days, whereas B alone can do it in 21 days. B works alone on day 1 while A works alone on day 2, and the process continues alternately till the work is completed. How many days in all does it take for the work to be completed?

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?