Verified Answer :

Make sure you know the formula pertaining to the question. 

1. c=2(pi)(r)
2. c=2(pi)(d)

r= radius 
d= diameter
c= sircumference

So we are given that the circumference of a circle is 12.3pi and the radius is unknown. 

So let's plug in the known values 

**we use the formula with the radius, becuase we are looking for the radius. 

c=2(pi)(r)
12.3(pi)=2(pi)(r)

divide each side by pi

12.3=2(r)

divide each side by 2

r=6.15 in.

Answer:

the answer is c, i just got it right

Step-by-step explanation: 6.15 inches, because it is the radius.