If 25 people working 10 hours a day can complete 2 units of work in 7 days, then how many days will it take 14 people working 10 hours a day to complete 20 units of work?

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?