Radius

The radius of a circle is the distance from it's center to it's edge.

It is often represented by the letter R.
The formula for the radius of a circle is:
R = C / 2

where C is the circle's circumference and

is 3.14 (approximately).
If you know the circle's diameter (D) then:
R = D / 2

So, if a circle's diameter is 30 cm, what is it's radius? _______ cm.