Two inlet pipes can fill a cistern in 30 minutes and 45 minutes respectively, and an outlet pipe can empty 20 gallons of water per minute. All three pipes working together can fill the empty cistern in 45 minutes. What is the capacity (in gallons) of 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?