An asteroid of mass 2.0×105 kg , traveling at a speed of 36 km/s relative to the Earth, hits the Earth at the equator tangentially, and in the direction of Earth's rotation. Use angular momentum to estimate the percent change in the angular speed of the Earth as a result of the collision.

I set up my equation like the following..

(5MaVa)/(2RMeWe), from change in angular velocity divided by angular vel of the earth. I used conservation of momentum, but I do not know how to get the Radius.