An astronaut has a mass of 76.0 kg. what is the astronaut's stationary weight at a position 8960 kilometers above earth's surface? note: earth's radius is 6380 km.

I'll take the gravitational constant G to be 6.67x10^-11 in this. I will also be using the mass of the earth as 5.972x10^24 (there might be a way to solve this without knowing the mass of the Earth but it has escaped me, if anyone wants to help me out on this then feel free).

We can calculate the gravity of the earth at the distance above it using 
g=mG/r^2

Substituting in, we get

g=(5.972x10^24)x(6.67x10^-11)/(6380000+8960000)^2
=1.69 to 3sf

We also know that w=mg, so the weight of the astronaut is w=76x1.69=128.44N = 128N to 3sf