There are two pipes A and B, each of which can fill a tank in 20 hours. When both pipes are opened together, due to a leakage, it is found that it takes 2 hours more to fill the tank. If the tank is completely full, in what time will the leakage empty the tank?

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?