The formula for circumference is C = 2πr. Just plug in the radius. C = 2π2. 2 times 2 is 4. So, multiply 4π, which is 6.283185307 (rounded to the nearest billionths). Generally, you are supposed to round to the nearest hundredth. The 3 would round the 8 down, leaving 6.28. The unit used to measure the radius, so unless told otherwise by the problem, stick to km. This results in 6.28 km being your final answer.
