sqrt ((6.674e-11*90*5.974e24)/(6.674e-11*90*5.974e24/(6.371e6)^2-.00424))

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.