Shear stress in a sign post

A 6-m-long sign post is loaded by a horizontal force of 13.5 kN. The rectangular structural tube is 200 mm wide and 150 mm deep. The wall thickness of the tube is 10 mm on each of the four sides.

Compute the shear stress at point H in the wall of the structural tube at a distance of y = +30 mm from the centroidal axis (see the sketch).