Hello,

Since the satellite is stationary, it has same angular velocity as that of earth.

Thus \omega=\dfrac{2\pi}{T}=\dfrac{v}{r}ω=T2π=rv

\implies v=\dfrac{2\pi r}{T}v=T2πr

The centripetal acceleration arises from the gravitational force earth exerts on satellite.

\implies \dfrac{mv^2}{r}=\dfrac{GMm}{r^2}rmv2=r2GMm

Eliminating vv from above equations gives

r=(\dfrac{GMT^2}{4\pi ^2})^{1/3}r=(4π2GMT2)1/3

Hope this helps, Good Luck.