An aluminum $(E=70$GPa $)$ column was built into the ground as shown in the figure below. Its length, L$,$ is given as $2\mathrm{.}2$ m $,$ and it is under axial compressive load P$.$ The dimensions of the cross$-$section are $b=210$ mm and $d=280mm.$

What is the critical load to buckle the column?

$6700$ kN

$7700$ kN

$13690$ kN