The answer is radius=3.5. To find the radius you can use two methods.
1. Divide the circumference by Pie, that will give you the diameter and since that would be 7 and the radius is half of the diameter it would be 3.5.
2. Divide by he circumference by 2(Pie) so 22/2Pie would give you 3.5(radius). These methods are just the backwards process of finding the circumference.
First method used C=2*(diameter)
Second method used C= 2*(Pie)*Radius