The length, breadth and height of a room are 5 m, 4 m and 3 m respectively. Find the cost of white-washing the walls of the room and ceiling at the rate of $ 7.50 per m^2.

Ceiling = 5 x 4 = 20 m²

The 4 walls = ( 5 + 5 + 4 + 4) x 3 = 18 x 3 = 54 m²

Total area = 20 + 54 = 74 m²

1  m² = $7.50
74 m² = $7.50 x 74 = $555.

Answer: It will cost $444 to white-wash the walls and the ceiling.