Questions: Find the radius of a circle with a circumference of 36π.

The answer is B: 6.

To find the radius of a circle given its circumference, we can use the formula for the circumference of a circle, which is:

\[ C = 2\pi r \]

where \( C \) is the circumference and \( r \) is the radius.

Given that the circumference \( C \) is \( 36\pi \), we can set up the equation:

\[ 36\pi = 2\pi r \]

To solve for \( r \), we divide both sides of the equation by \( 2\pi \):

\[ r = \frac{36\pi}{2\pi} \]

\[ r = \frac{36}{2} \]

\[ r = 18 \]

Therefore, the radius of the circle is 18. However, this contradicts the options provided. Let's re-evaluate the options and the calculation.

Given the circumference \( 36\pi \):

\[ 36\pi = 2\pi r \]

Divide both sides by \( 2\pi \):

\[ r = \frac{36\pi}{2\pi} \]

\[ r = 18 \]

It seems there was a mistake in the initial interpretation. The correct calculation should be:

\[ r = \frac{36}{2} \]

\[ r = 18 \]

Thus, the correct answer is indeed A: 18.