Calculating Satellite Speed Based on Orbit Period

[phobia]

Homework Statement

A satellite is in a circular orbit about the Earth (M = 5.98 x 1024 kg). The period of the satellite is 7.12 x 104 s. What is the speed at which the satellite travels?

2. The attempt at a solution
I used the equation:

http://img171.imageshack.us/img171/7176/math062gg0.gif

Re-arranged it to isolate r:

http://img74.imageshack.us/img74/9274/math065rr5.gif

After I got radii, i solved for velocity:

http://img171.imageshack.us/img171/3975/math053pd6.gif

My answer: 1.26x10^7 m/s
Teacher: Incorrect

Note: The numbers in the equations are not the actual ones i used.

 

[learningphysics]

The equations seem right to me. Seems like something went wrong when plugging in the numbers. What are the actual numbers you used?