16 workers working 6 hours a day can build a wall of length 150 m, breadth 20 m and height 12 m in 25 days. In how many days can 12 workers, working 8 hours a day, build a wall of length 800 m, breadth 15 m and height 6 m?

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?