Homework Statement

Communications satellites are placed in orbits such that they rotate the Earth once every 24.0 hours. Determine how high above the Earths surface these satellites must be placed.

Homework Equations

GM/4(3.14 squared) times T squared

The Attempt at a Solution

so i know that first i have to get the radius by using GM/4(3.14 squared) times T squared, and then subract the earths radius from that, but what would be the M in that equation?