How much HO track do I need...?

Thanks very much guys!

Ok, so...

If I want black track and not gray...

What exactly do I need to make a 72" diameter "circle"?

Am I right in understanding that there is no way to make a 72" diameter perfect circle?

And I will need some curved pieces and some straight pieces?

Thanks for all of your help, I really am new to this!

Hey, thanks for everyone's help...

But, I am getting a little discouraged...

I found the engine and tender I want... the Athearn Big Boy...

Now it seems finding the rest of what I want is, well, discouraging...

I would like to add 2-3 black passenger cars, but can not find black unless I go to e-bay and get old cars that I have to assemble myself...

And I do not understand this track stuff...

You can make a circle using straight pieces, but a rectangle is just all curved pieces - that makes no sense to me, lol... It would seem that a circle would use all curved pieces and a rectangle would use straight pieces...

Or flex track...

HELP!