Determine the number of vacancies per cm^3 needed for a BCC iron crystal to have a density of 7.87 g/cm^3. The lattice parameter of the iron is 2.866x10^-8 cm and the atomic weight of the iron is 55.847 g/mol. Given: Avogradro's number, N=6.022x10^23 atoms/mol Help please? i have no idea how to solve this question :( im gona have my first test for material science on wednesday!!