Answer:
Step-by-step explanation:
A circumference of a circle can be determined by this: 2*pi*r
We're given the diameter. Divide that by 2 to get the radius.
6.45/2 = 3.225
Now multiply that by 2*pi. That gives us 2 * 3.14 * 3.225 = 20.253.
This could've also been done easier by doing pi*d where d is the diameter and you give the answer by multiplying them both. Also works, but the above formula is just key to many things and can also be used to derive the simpler one. Hope it helps! :)