3. Some hypothetical alloy is composed of 12.5 wt% of metal A and 87.5 wt% of metal B. If the densities of metals A and B are 4.27 and 6.35 g/cm3, respectively, whereas their respective atomic weights are 61.4 and 125.7 g/mol, a. Determine whether the crystal structure for this alloy is simple cubic, face-centered cubic, or body-centered cubic. Assume a unit cell edge length of 0.395 nm. b. Determine the number of atomic sites in the alloy in atoms/m3. c. If the vacancy concentration at 550 oC is 4.52 x 10 -6 determine the activation energy for vacancy formation.