How can I find the radius of a circle?

How do I find the radius of a circle with the circumference?

• I was given the circumference of a circle, 16pi, and need to find the radius of the circle. How do I do that? please give me the steps and the answer. Thank you! and can you also tell me how to when given the area instead of the circumference. For instance, I was given the area 81pi, what is the radius, step by step please.

• Answer:

  C = 2 pi r, so 16 pi = 2 pi r, so 8 pi = pi r, so r = 8 A = pi r^2, so 81 pi = pi r^2, so 81 = r^2, so r = 9