What is the diameter of planet x. Planet X's moon is 1/3 of the size of it. The diameter of planet X is 5235.98

I think Anonymous is saying that planet x's moon has a diameter of 5235.98. Anonymous, you better go to formulary>sphere. Don't forget to multiply by 3.

You are aking:  What is the diameter of planet X?

But, in the next line, you are saying:  The diameter of planet X is 5235.98.

So, the diameter of planet X is 5235.98.