I just did some work for this, and I believe the correct answer is b. 7%.
You can download answer here
tinyurl.com/wtjfavyw
4(4)-7
16-7
9
Hope this helped!
The radius becomes the side length of six isosceles triangles. Assuming each triangle is equilateral, the height of each triangle is 4*(sqrt3).
The total area is 6 times .5*4(4sqrt3)=41.56121938 or 42 square feet
Answer: 75.36mm
i don’t know how to explain it i’m sorry