The Question is kind of Simple. "Find the angular speed of a point on the Earth's surface". That is all that is given, assuming the the radius is 6400km. How do I set this up???
Ok. Sorry for my last post, it was bad.
In one day (24 hours), the Earth has done a revolution, that is if you were on its surface, you would have done $\displaystyle 2\pi r$ kilometers.
It's angular speed is $\displaystyle \frac{2\pi rad}{24 hours}$. 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 $\displaystyle \frac{rad}{s}$.
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 $\displaystyle 2\pi$ 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.