So I want to find the number of rotations the tire makes in one second, and to do that I divide the velocity of the car by the circumference of the tire. (I think)

is the circumference of the circle in meters.

is the number of rotations per second.

So the circle makes approximately 138.5 rotations per second. I know that an entire circle is

radians so I just multiple 138.5 by

and that works out to be 870.22 radians/s.

The answer is supposed to be 86.83 radians/s and I don't know what I'm doing wrong. Could someone please explain?

I have no idea how to start this one. Help!

(Headbang)