A $30-$in$-$wide by $0\mathrm{.}110-$in$-$thick by $140-$in$-$long steel sheet is to be formed into a hollow section by being bent through $360$ degrees and having the long edges welded together. Assume a cross

$-$ sectional medial length of $30$ in$.$ If the maximum shear stress must be limited to $17$ ksi, determine the maximum torque that can be carried by the hollow section if $($a$)$ the shape of the section is a circle $($b$)$ the shape of the section is an equilateral triangle $($c$)$ the shape of the section is a square $($d$)$ the shape of the section is a rectangle measuring $9\mathrm{.}0$x$6\mathrm{.}0$ in$.$