The image shows a question about a square with an area of 81 square units. To solve this, you need to find the side length of the square.

1. Formula for the area of a square: $\text{Area} = \text{side length}^2$

   In this case, the area is 81, so: $\text{side length}^2 = 81$

2. Solve for the side length: Take the square root of both sides to find the side length: $\text{side length} = \sqrt{81}$

   Since $\sqrt{81} = 9$, the side length of the square is 9 units.

Would you like more detailed steps or explanations on square roots or other related topics?

Here are 5 related questions:

1. How can we calculate the square root of any number manually?
2. What is the area of a square with a side length of 7 units?
3. How is the concept of square roots applied in real-world problems?
4. What is the cube root of 81?
5. How do we find the side length of a rectangle if only the area and one side are known?

Tip: Always check that the square root is positive for side lengths since a side length cannot be negative.