At what distance above earth would a satellite have a period of 125 min?

Rw^2 = GmM/r^2

Leads to

w^2 r^3 = GM

(2pi / T) ^2 r^3 = GM

4pi^2 r^3 = GM T^2

r^3 = GM T^2 / 4pi^2

Work out r^3 then r.

T = 125 min = 125 (60) = 7500 s

R = 6.38E6 m

m = 5.97E24 kg

G = 6.673E-11

r = 8279791.78 m

Since r = radius R of Earth + height above urface, h

h = r - R = 8279791.78 - 6.38E6 = 1899791.78 m

h = 1899.79178 Km