1. **Problem statement:** An aquarium is in the form of a cuboid with external dimensions 80 cm x 80 cm x 40 cm. We need to find the area of paper required to cover the bottom, side faces, and back face. 2. **Formula and explanation:** The surface area of a cuboid is given by $$2(lb + bh + hl)$$ where $l$, $b$, and $h$ are length, breadth, and height respectively. Here, we only need the area of the bottom, two side faces, and the back face. - Bottom area = $l \times b$ - Two side faces area = $2 \times (b \times h)$ - Back face area = $l \times h$ 3. **Substitute values:** - Bottom area = $80 \times 80 = 6400$ cm² - Side faces area = $2 \times (80 \times 40) = 2 \times 3200 = 6400$ cm² - Back face area = $80 \times 40 = 3200$ cm² 4. **Total area of paper needed:** $$6400 + 6400 + 3200 = 16000 \text{ cm}^2$$ 5. **Convert to square meters:** $$16000 \text{ cm}^2 = \frac{16000}{10000} = 1.6 \text{ m}^2$$ **Final answer:** The area of paper needed is $1.6$ square meters.