The dimensions of a room are 12.5 m by 9m by 7m. There are 2 doors and 4 windows in the room; each door measures 2.5 m by 1.2 m and each window 1.5m by 1 m. Find the cost of painting the walls at Rs. 3.50 per square metre.

Explanation

To solve the problem step by step, we will calculate the area of the walls of the room, subtract the area of the doors and windows, and then find the cost of painting the remaining area.

### Step 1: Calculate the area of the four walls of the room.

The formula for the area of the four walls of a cuboid (room) is given by:
\[ \text{Area of 4 walls} = 2 \times h \times (l + b) \]
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