Figure $2$ shows a thin$-$walled cross$-$section subjected to a vertical shear force V $=200$ N$.$ The dimensions of the thin$-$walled cross$-$section are indicated in the figure. The vertical shear force V is applied at the shear centre S of the cross$-$section. For simplicity, all calculations can be based on the centre lines,

a$)$ Calculate the shear stresses at section a$-$a and section b$-$b$.(10$ points$)$

b$)$ Calculate the distance $\text{'}$e$\text{'}$ between the shear center S and the centerline of the web. $(10$ points$).$