# Angular Speed...

In one day (24 hours), the Earth has done a revolution, that is if you were on its surface, you would have done $2\pi r$ kilometers.
It's angular speed is $\frac{2\pi rad}{24 hours}$. You realize that the angular speed of Earth is independent of the radius, so the radius they gave you doesn't matter.
Now just convert the answer into $\frac{rad}{s}$.
EDIT: You set up this by thinking like that : I consider the Earth as a circle (to simplificate a lot). Compare it with the unit circle and the angles in radian. You know that $2\pi$ radian is the whole circle, that is an angle of 360°. You also know that the Earth will turn this angle in about 24 hours.