Problem $06\mathrm{.}053-$ Shearing stress in an extruded beam

An extruded beam has a uniform wall thickness $t.$ Denoting by $V$ the vertical shear and by A the cross$-$sectional area of the beam, express the maximum shearing stress as $I_{\text{m}\text{a}\text{x}}=k(\frac{V}{A})$ and determine the constant $k$ for each of the two orientations shown.

The constant $k$ for the orientation shown in $a$ is

The constant $k$ for the orientation shown in $b$ is