A 0.250 mm thick strip of calcium metal is placed in a perpendicular magnetic field of 5.00T. When a current of 117mA is passed along its length, a Hall voltage of 5.00 muN is measured across its width. If the charge carriers in calcium are electrons, how many free electrons per calcium atom are there? Note that calcium metal has 2.30 x 10^28 atoms/m^3.