Answer:
The length of ED, or the diameter, is 8
Explanation:
As the other person explained, CF is the radius, as the radius is from the centermost point to the edge. I also see that ED is the diameter, as the diameter is from edge to edge, going through the centermost point. Therefore, since the diameter is double the radius, we can solve this with the following equation:
2 * r = d, where r is radius and d is diameter.
2 * 4 = d
8 = d