If 7 maids clean 7 floors in 7 hours working with 7 robots, how long would it take 3 maids to clean 3 floors working with 3 robots?

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?