its a square, so all the sides are equal. Also, since the area of a square (rectangles) is equal to the height times the length, which are both the same, the area of the square is equal to x², where x is the length of any one side of the square, x²=256. now you square root both sides of that equation, x=√256, and the square root of 256 is 16.
Tl;Dr: each side is 16 feet long.
