It’s been awhile since I’ve done a problem like this but I believe it’s solved as below:
The area of a circle is equal to πr2. That will tell you the entire area of the circle. Then you would need to divide that by 2 to get the area of the 180° arc.
So, the area of this circle is 153.94 square meters. If you divide that by 2 (since 180° is half of a circle) you would get 76.97 square meters.