The formula for the perimeter of a square is P = 4s, where s is the length of one of the four (4) congruent sides of the square.
The formula for the area of a square is A = s², and we're given that the area of a square, whose perimeter we're trying to find, is 36 sq. units; therefore, we have:
A = s²
36 sq. units = s²
√(36 sq. units) = √s²
6 units = s (Note: We used the positive square root (6) rather than the negative square root (-6) since you physically can't have a negative length!)
Therefore, ...
P = 4s
P = 4(6 units)
P = 24 units is the perimeter of a square whose area is 36 square units