Calculate the earth's gravity force on a 65 kg astronaut who is repairing the hubble space telescope 600 km above the earth's surface

Let Fgrav=earth's gravity force(N)=asked,
m1=mass of astronaut(kg)=65kg,
m2=mass of the earth(kg)=5.98x10^24 kg,
G=universal gravitation constant=6.673x10^-11 Nm^2/kg^2

d1=distance from the surface of the earth to its center=6.38x10^6m
d2=distance of the astronaut from the surface of the earth=600km=6x10^5m
d=d1+d2, since the astronaut is above the surface of the earth
d=6.38x10^6m + 6x10^5m=6,980,000m

Working equation: Fgrav=(Gm1m2)/d^2
Fgrav=(6.673x10^-11 Nm^2/kg^2)(65kg)(5.98x10^24 kg)/(6,980,000m)^2
Fgrav=532.38 N

The correct answer is  "c".  it is "c" because melting is an endothermic change, and endothermic get's energy from surroundings.