A 250 mm bar of 15mm x 30 mm rectangular cross-section consists of two aluminum layers, which are 5 mm thick each, brazed to a center brass layer of the same thickness. If the bar is subjected to centric forces of magnitude P = 30 kN and knowing that EA = 70 GPa and EB = 105 GPa, determine the normal stress (a) in the aluminum layers, (b) in the brass layer.