A line segment is 8
Let the radius of a larger circle be X
The radius of a smaller circle is: Y = sqrt( X² - 4² )
The area of a larger circle A1 = X² * pi
The area of a smaller circle A2 = Y² * pi
The area of the green ring A3 = A1 - A2 
( I think that my dumb answer matches the question.) 
