Two pipes A and B can fill a cistern in 3712 minutes and 45 minutes, respectively. Both pipes are opened. The cistern will be filled in just half an hour, if pipe B is turned off after:

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?