The formula for diameter (Yes, diameter, stick with me here.) is d = c/π. Plug in your circumference; d = 28/π, which equals 8.912676813 rounded to the nearest billionth. The formula for radius is d/2. So, 8.91267813/2 is 4.456338407 (rounded to the nearest billionth) generally, you are supposed to round to the nearest hundredth. Unless the question says otherwise, the 6 rounds the 5 up, leaving you with 4.46 as the final answer.
