Final answer:
To find the cost of coloring the walls, calculate the area of the walls by finding the perimeter of the room and multiply it by the height.
Step-by-step explanation:
To find the cost of coloring the walls, we need to calculate the area of the walls first. The area of the walls can be calculated by finding the perimeter of the room and multiplying it by the height. Given that the length of the room is three times its width, let's assume the width is 'x'. So, the length will be '3x'.
The perimeter of the room is given by 2(length + width) = 2(3x + x) = 8x.
The area of the walls is given by perimeter x height = 8x x 4.5 = 36x.
The total cost of coloring the walls is calculated by multiplying the area of the walls by the cost per square meter which is Rs 25. So, the total cost is 36x x 25 = 900x.