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

Question

$$(a)\;10\;hours \quad (b)\;\frac{6}{\sqrt 2}\;hours \quad (c)\;6\;hours \quad (d)\;6 \sqrt 2 \;hours$$