$($will be solved by virtual work method$)$Knowing that the constant of the spring CD is k and that the spring is not stretched when the bar ABC is horizontal, determine its value corresponding to the equilibrium for the given data.

A$)$ P $=300$ N$,1=400$ mm$,$ k $=5$ kN$/$m B$)$ P $=330$ N$,1=380$ mm$,$ k $=3\mathrm{.}5$ kN$/$m