Question

The circumference of a coin is 8π What is the radius? What is the diameter?

Answer 1

Find the radius first.
Circumference of a circle:
$=2 \pi r$
$8 \pi =2 \pi r$$\frac{8 \pi }{2 \pi } = r$
r=4

diameter = radius x 2
4x2 = 8

Answer 2

The constant π is defined as C/d, meaning pi is the constant when the circumference of a circle is divided by the diameter of that circle.  Anyway:

πd=C  divide both sides by π

d=C/π, if C=8π then

d=8π/π

d=8

So the diameter is 8 units.