1. The problem states that we have a square plot of land with an area of 81 m², and we need to find the length of one side of the square. 2. The formula for the area of a square is: $$\text{Area} = \text{side}^2$$ 3. We know the area is 81 m², so we set up the equation: $$\text{side}^2 = 81$$ 4. To find the side length, take the square root of both sides: $$\text{side} = \sqrt{81}$$ 5. Simplifying the square root: $$\text{side} = 9$$ 6. Therefore, the length of one side of the square plot is 9 meters. This means the terrace adjacent to one side of the square is 9 meters long.