$7-$d$)$ A beam with the shown cross section is subjected to a vertical shear force, $V=180$ kN $,$ calculate:

a$)$ The average shear stress in the beam.

b$)$ The maximum shear stress in the beam.

Given $\frac{?}{\text{b}\text{a}\text{r}}(y)=60mm,I=27{10}^{6}m{m}^4$