Find the surface area of a sphere whose radius is 2.1 cm.

19 The length of a cinema hall is 20 m and breadth is 16 m. The sum of the areas of floor and flat roof is equal to the area of four walls. Find the height and volume of the hall. 20 A cone is made from a metal sheet in the form of a sector of a circle. If the radius of the circle is 14 cm and the sector angle is 60°, find the radius of the base, slant height and the height of the cone formed. 22 How many metalboxes of size 8 cm × 5 cm × 3 cm can be packed in a cardboard box of size 40cm × 40cm × 21cm. 23 A closed cuboid water tank is made of steel sheet that is 2.5 cm thick. The outer dimensions of the tank are
2.15 m × 1.5 m × 1.1 m. Find the capacity of the tank, and the volume of steel used to construct it. Also find the total surface area of the tank.