Answer:
15371.68
Explanation:
First you need to find the area of the semi circle so for that you just have to find the area of a whole circle using the diameter and then divide it by two because it is a semicircle. The area of the semi circle is pi * 20^2 / 2 which equals 628.32. The all you have to do is subtract that from the area of the door which is 16000.