A can complete a certain work in 30 days. He started the work alone. After 4 days, B joined him and the whole work was completed in 10 days from the beginning. B alone can complete one-third of the same work in how many days?

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?