Explanation:
You divide the polygon into smaller shapes, rectangles suit this best.
There will be 2 rectangles:
1st rectangle whose length is 24ft and its width is 11 ft (21-10=11).
2nd rectangle its length is 10ft and its width is 7ft.
You find the area of both rectangles. The formula of finding the area of a rectangle is length X width.
1st rectangle has an area of 264 ft² (24 X 11)
2nd rectangle has an area of 70ft² (10 X 7)
Add the area of the two angles to get the area of the polygon.