Given:
Area of the square = 81 square units.
Let's find the perimeter.
To find the perimeter of a square, apply the formula:
Perimeter = 4L
Where L is the side length of one side of the square.
To find L given the area, apply the formula:

Hence, we have:

Take the square root of both sides:
![\begin{gathered} \sqrt[]{81}=\sqrt[]{L^2} \\ \\ 9=L \\ \\ L=9\text{ units} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/9swi8m43pjv209z76gil680q5kbdtlw10m.png)
The length of one side of the square is 9 units.
To find the perimeter, substitute 9 for L in the formula for Perimeter of a square.
Perimeter = 4L = 4(9) = 36 units
Therefore, the perimeter of the square is 36 units.
ANSWER:
36 units.