### Instruction: The circumference of a particular circle is 18 cm. In square centimeters, what is the area of the circle? Express your answer as a common fraction in terms of $\pi$.### Response: Let's call the radius of the circle r.
And we know that the circumference of a circle is 2*pi*r.
That's right. So we can write the equation 18=2*pi*r.
So r=9/pi.
Now we can use that to find the area of the circle.
The area of a circle is pi*r^2.
So the area of this circle is pi*(9/pi)^2.
Which simplifies to 81/pi.