An object is orbiting earth at a height of $100$ $km$ from the surface. What's the period in seconds?

Gravitational Constant, $G=6.673\times10^{-11}$ $N$ $kg^{-2}$ $m^2$
Mass of the Earth, $M_e = 6\times 10^{24} $ $kg $
Radius of the Earth, $R=6400$ $km$

Hint: Do you know Kepler's third law?