Question $4$: Consider the following plane stress problem with isotropic and linear elastic material behavior of modulus of elasticity $($Young$\text{'}$s modulus$)E=200$GPa, Poisson's ratio $v=0\mathrm{.}25,$ and shear modulus $G=80$GPa. Use one $"$CST$"$ triangular element and give the elementary stiffness matrix then write the condensed equations of the primary variables in matrix form and in global coordinate system $x$ and $y.$ The triangular shape has a constant thickness of $0\mathrm{.}1$ m $,$ it is fixed at the vertical segment and subjected to external loadings as shown. Neglect the body forces.

$(3$ points$)$