You’re looking for the *circumference* of the crater. The definition of π is the ratio of the circumference of the circle to its diameter, or mathematically:
π = c/d
Which means that c = dπ. Our diameter is 3900 ft, which mean that our circumference is 3900π ft, or, using 3.14 as π, 3900(3.14) = 12,246 ft.
