How Much Force Keeps a Satellite in Orbit at Three Earth Radii?

[chiurox]

Homework Statement

What is the force of gravity acting on a 4500kg satellite when it orbits three Earth radii from the Earth's center?

Homework Equations

Gm1m2/r²
mass of the earth=5.98*10^24kg
radius of the earth=6370km

The Attempt at a Solution

This is a multiple choice question, with answers:
15000N
45000N
500N
1500N
5000N

However, what I get from plugging in is:
[(6.67*10^-11)(4500)(5.98*10^24)]/(3*6370)²
which equals roughly: 5.0*10^9 which is completely off any of the answers... can anyone help me?

hahaha, never mind! I forgot to convert the km to m... -_-

 

[Snazzy]

You're not using SI units for distance.