The area of a sector is given by
.. A = (1/2)r^2*θ . . . . . θ is the central angle in radians
The area of an isosceles triangle with legs length r is
.. A = (1/2)r^2*sin(θ) . . . θ is the angle between same-length legs
The shaded area is the difference between these
.. A = (1/2)r^2*(θ -sin(θ))
.. = (1/2)*(18.6 m)^2*(π*123/180 -sin(123°))
.. ≈ 226.3 m^2