Question

Suppose the circumference of a circle is 3 pi. What is the diameter?

Answer 1

This was asked already
c=pid or
c=2pir

use first one
c=3pi
3pi=c=pid
3pi=pid
divide by pi
3=d
diameter=3 units

Answer 2

$2\pi r~or~ \pi d$ so divide 3 by $/pi$