3 a) How the hardness of a mild steel specimen is determined using a Brinell hardness testing machine? b) A silicon wafer is doped with 3.00 x 1017 boron atoms/ m2 at 27C. The electron and hole mobilities of charge carriers are 0.35 m2 / V-'s and 0.68 m2 /V-ls-respectively. Calculate the electrical resistivity of the material