$(5)$ Two $300-mm-$long rectangular steel strips are placed together as shown in the figure below.

If the maximum allowable shear stress is $80$ MPa $,$ determine the maximum torque, angular

twist, and torsional spring rate. Compare these with a single strip of cross$-$section $30$ mm by

$4$ mm $.$ Solve this problem two ways: $($a$)$ Assuming the configuration is for shear stress in a

rectangular cross$-$section bar i$.$e$.$ using Eqs. $(3-40)$ and $(3-41),$ and $($b$)$ Assuming the

configuration is for open$-$thin$-$walled section analysis i$.$e$.$ using Eq$.(3-47).$ Compare and

discuss your results. $(5$ points$)$