A room has dimensions L=5m, W=3m, H=2.5m. A door has dimensions 1.5m by 0.9m. Calculate the area to be painted.

The formula for the area of the four walls of a rectangular room is $2(L \times H) + 2(W \times H)$, where $L$ is length, $W$ is width, and $H$ is height.
Given: $L = 5$ m, $W = 3$ m, $H = 2.5$ m.

$$\text{Area of walls} = 2(5 \text{ m} \times 2.5 \text{ m}) + 2(3 \text{ m} \times 2.5 \text{ m})$$ $$\text{Area of walls} = 2(12.5 \text{ m}^2) + 2(7.5 \text{ m}^2)$$ $$\text{Area of walls} = 25 \text{ m}^2 + 15 \text{ m}^2$$ $$\text{Area of walls} = 40 \text{ m}^2$$

The formula for the area of a rectangle is length $\times$ width.
Given: door dimensions are 1.5 m by 0.9 m.

$$\text{Area of door} = 1.5 \text{ m} \times 0.9 \text{ m}$$ $$\text{Area of door} = 1.35 \text{ m}^2$$

This is the area of the walls minus the area of the door.

$$\text{Painted area} = \text{Area of walls} - \text{Area of door}$$ $$\text{Painted area} = 40 \text{ m}^2 - 1.35 \text{ m}^2$$ $$\text{Painted area} = 38.65 \text{ m}^2$$

The total surface area that will be painted is $\boxed{\text{38.65 m}^2}$.

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For question 8, the problem statement is incomplete as it describes the object and its dimensions but does not ask a specific question (e.g., to calculate its volume, surface area, or mass).