For Platinum, the Hall coefficient $($RH$)$ is $-2\mathrm{.}00{10}^{-11}\frac{m^3}{C}.$ The resistivity is $10\mathrm{.}6{10}^{-2}m,$ and the density is $21\mathrm{.}45\frac{g}{c}{m}^3.$ Calculate: a$)$ The molality of electrons. b$)$ The number of electrons per atom. c$)$ If a current of $122$ mA flows through a sheet of $0\mathrm{.}00503$ cm thickness and $2\mathrm{.}12$ cm width, what is the value of the Hall potential in a magnetic field of $0\mathrm{.}500$ Tesla?