So we can figure out the radius from the circumference by saying, well, circumference is equal to 2 times pi times the radius of the circle. Or if you say 36 pi, which we're told is a circumference, is equal to 2 times pi times the radius. We can divide both sides by 2 pi. And on the left-hand side, 36 divided by 2 is 18. The pi's cancel out. We get our radius as being equal to 18 for this larger circle. This larger circle has a radius of 18.