A 24-in.-wide by 0.100-in.-thick by 140-in.-long steel sheet is to be formed into a hollow section by being bent through 360° and having the long edges welded (i.e., butt-welded) together. Assume a cross-sectional medial length of 24 in. (no stretching of the sheet due to bending). If the maximum shear stress must be limited to 18 ksi, determine the maximum torque that can be carried by the hollow 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 7.2 x4.8 in.