$4.$ A rectangular hollow beam $($ x$-$section : overall width w $=100$mm$,$ overall heighth $=$

$200$mm $,$ thickness t $=10$mm$)$ is subjected to a shear force of V $=60$kN$.$

$($a$)$ Compute the Qmax

$($b$)$ Calculate I $=?$

$($c$)$ Find the maximum shear stress and its location.