$k{x_0} + \sigma \frac{L}{2}Ag = Mg$
$\left[ {mass = density \times volume} \right]$
$ \Rightarrow k{x_0} = Mg - \sigma \frac{L}{2}Ag$
$ \Rightarrow {x_0} = \frac{{Mg - \frac{{\sigma LAg}}{2}}}{k} = \frac{{Mg}}{k}\left( {1 - \frac{{LA\sigma }}{{2M}}} \right)$


