Nah lol don't write both. I only know from hearing peoples answers.
You also didn't need to keep it in a quadratic, could've just took the roots of both sides.
You have to consider the original velocity as well.
So you work out initial GPE and initial KE, giving you total energy of the system. (1)
Then you work out final GPE at 500km altitude. (2)
Conservation of energy means that (2)+final KE is equal to (1)
Therefore you get value of final KE (at...