The area of a square is x^2 where x is the length of a side. If the area is 81, that means one side is sqrt(81). There are 4 sides so the perimeter is 4sqrt(81) = 4*9 = 36 cm.
Area of a square is A=side^2 since it a sqaure all sides are equal. 81=s^2 take the square root s=9 Perimeter is p=4s since all sides are equal So p=4(9) p=36
