Calculate the change in gravitational potential energy

[ASidd]

Homework Statement

A satellite of mass 750kg is changed from an orbital radius of 7000000m to a geostationary orbit of 4.2*10^4. Calculate the change in its gravitational potential energy

Mass= 750
Earths radius= 6380000m
Gravitational constant= 6.67*10^-11
Earths mass=6*10^24

Homework Equations

So I am guessing I have to use this equation
Final Gpe- initial Gpe
(-GMm/r)-(-GMm/r)

The Attempt at a Solution

(-6.67*10^-11*750*6*10^24/(7000000+6380000))-(-6.67*10^-11*750*6*10^24/(4.2*10^4*10^3)
= 1.69 *10^10

The answer is 3.7*10^8
I don't know where I went wrong?

 

[frogjg2003]

what is the new radius?