To solve for $r$ in the equation $C = 2\pi r$, follow these steps:

1. Start with the equation:
   $C = 2\pi r$
2. To isolate $r$, divide both sides by $2\pi$:
   $r = \frac{C}{2\pi}$

Thus, $r = \frac{C}{2\pi}$.

Would you like a more detailed explanation or any additional help?

Here are five related questions:

1. How do you calculate the circumference if the radius is given?
2. What is the value of $\pi$ and why is it important in these formulas?
3. How does the formula for circumference relate to the area of a circle?
4. What happens to the radius if the circumference doubles?
5. Can you derive the area of a circle using the formula for circumference?

Tip: Remember, the circumference formula $C = 2\pi r$ is specific to circles, and $\pi$ is a constant approximately equal to 3.14159.