15) Find the total surface area of a cast iron bar whose length, width and height are 20m, 15m and 12m.

16) What is the formula for total surface area of a cylinder?

17) What is the volume of a rectangular tank of 30 m length, 20m width and 10m height?

18) What is volume of the cylinder whose radius is 7 cm and height 12 cm?

19) What is the volume of sphere of radius 7 cm?