Diameter

The diameter of a circle is the width of the circle.
It is often represented by the letter D.
The formula for the diameter of a circle is:
D = C/

where C is the circle's circumference and

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

So, if a circle's radius is 15 cm, what is it's diameter?