A crater shape should look like a circle. Then, the distance around the crater would be the area of the circle. To answer this question, you need to know how to calculate circle area. Since the diameter is 4100ft and radius is 1/2 of diameter, then the area should be:
Circle area= 2* 3.14 * radius= 2 *3.14 * 1/2 * 4100ft= 12874ft