Answer: 87.92.
Step-by-step explanation: To find the circumference of a circle, you need the following equation:
2 x π x r, where π is ≈ 3.14 and r is the circle's radius. If you are ever given the diameter instead of the radius, just cut the diameter in half. In this case, the diameter was given, so we need to cut 28 in half, which makes 14. Your equation should look like this:
2 x 3.14 x 14 ≈ 87.92.
Hope this helps! :)