Period = 24 hours.
Thus using Keplers 3rd Law (r^3/T^2 = GM/4(Pi)^2)
Solving for r we get
r = 42,298km (this is radius of the earth + altitude)
Rather than assume radius of Earth, wedetermine radius of the Earth, we use the formula for 'g' --> g=GM/r^2 (should derive this first)...