Answer:
Option 3 - 9 feet.
Step-by-step explanation:
Given : Ariel's garden is planted in the shape of a square and has an area of 81 square feet. If she plans to put a fence around the perimeter of the garden.
To find : How much fencing will she need?
Solution :
The area of the garden square is 81 square feet.
The formula of area of square is 



The side of the square is 9 feet.
The fence around the perimeter of the garden is

So, The fence around the perimeter of the garden is 36 feet.
Therefore, Option 3 is correct.