To calculate the surface area of Monica's room, we will consider the walls, the ceiling, and the floor.
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Calculate the area of the two walls that are 20 ft long and 9 ft high: \[ \text{Area of two walls (20 ft long)} = 2 \times (20 , \text{ft} \times 9 , \text{ft}) = 2 \times 180 , \text{ft}^2 = 360 , \text{ft}^2 \]
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Calculate the area of the two walls that are 15 ft wide and 9 ft high: \[ \text{Area of two walls (15 ft wide)} = 2 \times (15 , \text{ft} \times 9 , \text{ft}) = 2 \times 135 , \text{ft}^2 = 270 , \text{ft}^2 \]
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Calculate the area of the ceiling: \[ \text{Area of the ceiling} = 20 , \text{ft} \times 15 , \text{ft} = 300 , \text{ft}^2 \]
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Calculate the area of the floor: \[ \text{Area of the floor} = 20 , \text{ft} \times 15 , \text{ft} = 300 , \text{ft}^2 \]
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Total surface area to paint: \[ \text{Total surface area} = \text{Area of two longer walls} + \text{Area of two shorter walls} + \text{Area of ceiling} + \text{Area of floor} \] \[ = 360 , \text{ft}^2 + 270 , \text{ft}^2 + 300 , \text{ft}^2 + 300 , \text{ft}^2 \] \[ = 1,230 , \text{ft}^2 \]
Thus, the total surface area of the room that will be painted is 1,230 square feet.