$(20$ Marks$)$

The thin walled section is subjected to shear forces as shown in the figure.

a$)$ Using "thin walled theory" determine the shear flow and shear stress at points $a,c$ and $d$ if $Vy=30kN$ and $Vx=0kN,$ Show the shear flow on a diagram of the cross section in your solution.

b$)$ Using "thin walled theory" determine the shear flow at points $b,c$ and $d$ if $Vy=0kN$ and $Vx=30kN,$ Show the shear flow on a diagram of the cross section in your solution.

NOTE: Use total areas to calculate the moment$($s$)$ of interia for the cross section