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 the ceiling at the rate of Rs 7.50 per m².

Lenght of room l = 5 m, breadth b = 4 m and height h = 3 m
Area of four walls and ceilling = Total surface area of room – area of floor
= 2(lb + bh + hl) – lb
= 2(5 × 4 + 4 × 3 + 3 × 5) – 5 × 4 m²
= 2(20 + 12 + 15) – 20 m²
= 2(47) – 20 m²
= 94 – 20 = 74 m²
Therefore, the area of four walls and ceilling = 74 m²
Hence, the cost of white washing the walls of walls of the room and the ceilling
= Rs 7.50 × 74 = Rs. 555.00