Problem $6$

Two forces P$1$ and P$2$ are applied to end D of lever ABD. Determine

$($a$)$ an equivalent force$-$couple system at the center of the transverse section passing through $H.$

$($b$)$ the normal and shearing stresses on an element at point $H$ having sides parallel to the $x$ and $y$ axes,

Please solve and help me understand