We can use this formula: C = 2 *

* r
We can't use the diameter in this formula. We have to use the radius. And the radius is half of the diameter.
9 / 2 = 4.5
And we'll also use 3.14 for [tex] \pi [/text].
Plug in all the values:
C = 2 * 3.14 * 4.5
C =
28.26
So, the circumference is 28.26.