3.36x10^6 N
The radius of Earth is 6371 km.
NOTE there was a subtle error on the numbers going into
this question; the “radius” value one should use for the
F = GMm/r^2 equation should be the distance between the
centers of two objects. You will get answer “D” if you use the
250km given as the radius for that equation. Most of you did
that appropriately so this question was graded and left in.
In reality, the radius of Earth itself is 6371 km so the ISS
certainly isn’t orbiting at 250km from Earth’s center (it would
be floating around in Earth’s core)! Here for the solution I’ve
fixed the numbers in the problem, and shown the calculation
with a weaker force of gravity, and the radius used in the
equation is R_earth plus the altitude of the ISS. The answer,
by the way, is the approximate mass of the real ISS!