An aluminum sheet (width = 500 mm, thickness = 4 mm and length = 2 m) must be transformed into a hollow profile by bending it 360 and welding the long edges together. The median length of the cross section is assumed to be 500 mm (without stretching of the sheet due to bending). If the maximum shear stress must be limited to 80 MPa, determine the maximum torque that can be supported by the hollow profile 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 of 150 100 mm.