The formula for the area of a semicircle is equivalent to the area if it were a circle divided by 2. Since the bottom edge of the window is 36 inches long, this means that its diameter is also 36 inches long. This gives an area of 508.94 square inches.
The solution is:
A = Acircle/2 = pi*r^2/2 = pi*(18)^2/2 = 508.94 in^2
