Question $6)$ A hollow triangular cross$-$section tube rod is subjected to a concentrated torsional moment of $\backslash (\backslash$mathrm$\{$Mb$\}=10\backslash$mathrm$\{$kNm$\}\backslash )$ at its B end, as shown in the figure. Calculate the maximum shear stress and the rotation $\backslash (\backslash$Omega$\_\{\backslash$mathrm$\{$AB$\}\}\backslash )$ of the B end relative to the clamped A$,$

a$)$ for a closed tube cross$-$section.

b$)$ for an open tube cross$-$section.

$($The material's shear modulus is $\backslash (\backslash$mathrm$\{$G$\}=\backslash$mathbf$\{80\}\backslash$mathbf$\{$G P a$\}\backslash )).$