A meteor crater is 3900 feet in diameter. Approximate the distance around the crater. Use 3.14 for π.

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.