A rectangular tank having a base of 80 m by 50 m and depth of 7 m is full of water. In how much time can the water be emptied by a pipe whose cross-section is a square of side 25 cm, if the water runs through the pipe at the rate of 20 km per hour?

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?