Rocket Orbit A-Level Question

Hi,
I was wondering whether anyone could help me with the following question which I am finding it impossible to get the answer for. The answer is said to be C, but after calculating the change in GPE I've already got something larger than that answer. I guess the next step is to add on work done to give it kinetic energy for the orbit but that's only going to make the answer even bigger!
Thanks in advance for your help!
PS I know this question has appeared previously on the forum but the explanations there aren't helping me

The question says the orbit is 18000 m above the centre of the Earth.
Your calculation assumes 18000 m above the surface.

Thank you, I hadn't noticed that.
However, using that value gives me 6x10^9 which is again too large if the correct answer is C?

You're right. In fact all the answers given seen unreasonable small, Could be a typo? This article shows a slightly different calculation to yours, which would actually give a somewhat bigger answer. I think the difference is accounted for by the extra kinetic energy required to remain in orbit compared with the energy just to attain the necessary altitude (as you mentioned in your first post).