Rinku has built a cuboidal water tank in his house the top of water tank is covered with an iron lead, He wants to cover the inner surface of the tank including the base with tiles of size 10 by 10 cm . If the dimensions of water tank are 180cm , 120cm , and 60cm and cost of tiles is Rs.480 per dozen , then find the amount required for tiles.

Explain how you got the FORMULA?