What you need to do is separate the shape of the field into one rectangle and two halves of a circle.
It seems there is an error in your answers, because the area of the rectangle is 50,000. Because 50 x 100 is 50,000.
The area of the circle is 1,963.495... because A = (pi) r^2.
Add 5,000 (it should be 50,000 but whatever) to 1,963 and you get...
So the answer is C, 6,963