Answer:
x^2 = a
Explanation:
Since the window is a square, that means all sides equal to the same thing. If you don't understand; if we look at all the sides you'll see that they all are the same in size. Let's say the number for x is 10. You'd multiply 10 by 10 and get 100 square inches.
x^2 (or x * x) will equal to the area of the square window.