Note: perform all calculations in mm and provide numerical results to three significant figures. The cross section of the longitudes is an I-beam. The details are given in Figure 11. 120 10 10 330 Figure 11 I-beam dimensions (dimensions in mm) 10 a. Perform a manual calculation to show that the second moment of area about the horizontal axis through the centre of area for the hollow section in Figure 11 is 99.3x10 mm (to 3 .). Show all your workings. b. Keeping the main height dimension of 350 mm and the wall thicknesses of 10 mm but now using a hollow rectangle. Calculate what width of hollow rectangle would be required so that the second moment of area about the horizontal axis through the centre of area remains the same.