Our first step is to figure out what formulas are needed for diameter, circumference, and area of a circle.
Diameter is simply twice the size of the radius so:
2 radius = 2 40 feet = 80 ft.
Circumference = 2 pi radius = 80 ft pi
If we say that pi = 3.14, then:
circumference = 251.2 ft.
Area = pi radius^2 = pi 1600 ft^2
Once again, if we assert pi = 3.14, then:
area = 3.14 1600 ft^2 = 5024 ft^2.