The sum of the inner and the outer curved surfaces of a hollow metallic cylinder is 1056 cm² and the volume of the material is 1056 cm³. Find its internal and external radii. Given that the height of the cylinder is 21 cm.

A tent is of the shape of a right circular cylinder upto height of 3 meters and then becomes a right circular cone with a maximum height of 13.5 meters above the ground. Calculate the cost of painting the inner surface of the tent at ₹ 4 per sq. meter, if the radius of the base is 14 meters.

A pool has a uniform circular cross section of radius 5 m and uniform depth 1.4 m. It is filled by a pipe which delivers water at the rate of 20 litres per sec. Calculate, in minutes, the time taken to fill the pool. If the pool is emptied in 42 min. by another cylindrical pipe through which water flows at 2 m per sec, calculate the radius of the pipe in cm.