Please solve it wih all calculation:$)$ Not just the foulas please :)

The figure shows the supporting principle for a wooden quay structure, where continuous beams with a center distance of $5$m are supported by $3$ columns with different cross$-$sections, storage conditions and lengths.

The E$-$modulus of the material is set equal to $6000$ N$/$mm$2.$Dead load for the bridge deck is $2$ kN$/$m$2$ while payload is $5$ kN$/$m$2.$

a$)$ Calculate the design normal force in each of the three columns.

b$)$ Calculate the slenderness ratio and critical buckling load for each of the three columns. Compare with a$)$