The dimensions of a room are `20 ftxx 15 ftxx 12ft`. Find the cost of painting the walls of the room at rupees 20 per sq. ft.

Explanation

To solve the problem of finding the cost of painting the walls of a room with dimensions 20 ft, 15 ft, and 12 ft, we will follow these steps:

### Step 1: Identify the dimensions of the room
- Length (L) = 20 ft
- Width (B) = 15 ft
- Height (H) = 12 ft

### Step 2: Calculate the lateral surface area of the room
The formula for the lateral surface area (A) of a cuboid (which represents the walls of the room) is given by:
\[ A = 2 \times (L + B) \times H \]
Substituting the values:
\[ A = 2 \times (20 + 15) \times 12 \]

### Step 3: Simplify the expression
First, calculate \( L + B \):
\[ L + B = 20 + 15 = 35 \]
Now substitute this back into the area formula:
\[ A = 2 \times 35 \times 12 \]

### Step 4: Calculate the area
Now, calculate \( 2 \times 35 \):
\[ 2 \times 35 = 70 \]
Then multiply by the height (H):
\[ A = 70 \times 12 = 840 \text{ sq. ft.} \]

### Step 5: Calculate the cost of painting the walls
The cost of painting is given as 20 rupees per square foot. Therefore, the total cost (C) can be calculated as:
\[ C = A \times \text{cost per sq. ft.} \]
Substituting the values:
\[ C = 840 \times 20 \]

### Step 6: Perform the multiplication
Now, calculate the total cost:
\[ C = 840 \times 20 = 16800 \text{ rupees} \]

### Final Answer
The cost of painting the walls of the room is **16800 rupees**.

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