Where can a geostationary satellite be installed?

$A$ satellite is revolving very close to a planet of density $\rho$. The period of revolution of the satellite is

What is the time period of a satellite orbiting at a height $R$ above the Earth's surface?

Two satellites $A$ and $B$ are orbiting in circular paths of radii $4R$ and $R$ respectively. If the orbital velocity of satellite $A$ is $3V$,what is the orbital velocity of satellite $B$ (in $V$)?

$A$ geostationary satellite is orbiting the earth at a height of $6R$ above the surface of the earth,where $R$ is the radius of the earth. The time period of another satellite at a height of $2.5R$ from the surface of the earth is

$A$ body is moving in a low circular orbit about a planet of mass $M$ and radius $R$. The radius of the orbit can be taken to be $R$ itself. Then the ratio of the speed of this body in the orbit to the escape velocity from the planet is