A spherical planet with a diameter of 1600 km with a uniform density of 5200 kilograms per metre
If a space station is in a circular orbit 630 km above the surface of the world
What is its orbital velocity in metres per second?

Believe it or not, this is a question found on a kids site and my son has asked ME! to do it for him.
I haven't a clue, but would appreciate some help here and an explanation as to the answer would be First Rate. Thanks