Formula for area of a circle: area = pi r^2
Area of one small circle = pi x 3 ^2 = 9pi
There are two small circles so area is 2 x 9 pi = 18pi
Area of large circle = pi x 12^2 = 144pi
Area of shaded Reston is area of large circle - area of the two small circles:
144pi - 18 pi = 126pi sq.in.