A orbiting satellite stays over a certain spot on the equator of (rotating) Earth. What is the altitude of the orbit (called a "synchronous orbit")?
Write the equation for the period of a satellite in terms of the distance from the Earth's center. It is a special form of Kepler's Third law. Then set the period equal to 24 hours and solve for the distance from the center. Subtract the Earth's radius to get the altitude.
This reference may help: