1. Area of a circle is pi x R^2
Area = 3.14 x 18^2
Area = 3.14 x 324= 1017.36 sq. In.
The blade covers 122 out of 360 degrees.
1017.36 x 122/360 = 345 square inches.
2.
Like above.
Area =3.14 x 75^2 = 17,662.5 square feet
17662.5 x 80/360 = 3,925 square feet.