To find area, you multiply base x height. So to find base and height, you find the square root of 324(because this is a square). I am in 8th grade and I don't really know how to find the square root so I googled it(sorry).
sqrt of 324 is 18.
Double Check!
18
x18
144
+180
324
So each side is 18 inches.
hope it helps!