To find the radius \( r \) from the circumference formula \( C = 2\pi r \), you would rearrange the formula as follows:
- Start with the original formula: \( C = 2\pi r \).
- Divide both sides by \( 2\pi \):
\[ r = \frac{C}{2\pi} \]
Thus, the correct rearranged formula is \( r = \frac{C}{2\pi} \).
None of the provided responses match this correctly rearranged equation.