So there's a temptation to just use this 36 pi up here. We have to remember this was the circumference and we need to figure out the area of both of these circles. And so for area, we need to know the radius because area is pi r squared. 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.