Question regarding gravitational potential

[Sanosuke Sagara]

I have my question and solution in the attachment that followed.

[vincentchan]

do you know calculus? if yes, review the way you did dV/dr, if dr = (400000-39000) or (410000-400000), the answer will be closer, your second part is right....

[vincentchan]

the solution might expect you use the data table, so the number have some error....