The area of a circle is pi*r^2=a since we know the diameter is 24 and radius is half the diameter the r=12 so the area of the half circle = 1/2*pi*12^2 and the area of the square is simply base*height = 24*24 then the area with the missing portion must be 24*24-1/2*pi*12^2 = 576-72pi= approximately 349.8cm
