Suppose there's a hole through the center of the earth. An object is dropped through that hole from a height of $100$ $km$ from the surface. How long will it take to reach maximum height on the other side of that hole?

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

Note: Your answer should be in second.