Diameter = 23 ft
radius = diameter/2
radius = 23/2
radius = 11.5 ft
Area of the circle = pi*r~2
Area of the circle = 3.14¨11.5^2
Area of the circle = 3.14*132.25
Area of the circle = 415.27 ft^2
Area of the tunnel = area of the circle/2
Area of tunnel = 415.27/2
Area of the tunnel = 207.6 ft^2