Answer:
Perimeter of the windows is P = 4s, or (here) P = 4(x+9) ft.
Step-by-step explanation:
If the area of the square is x^2 + 18x + 81 (ft^2), then the length of one side is given by the square root of that, and is x + 9 (ft). Note that (x + 9)^2 = x^2 + 18x + 81.
The perimeter of a square window of side length s is P = 4s.
Here, the perimeter of the square is P = 4(x+9) (ft).
