Carbon dioxide is diffusing through nitrogen in one direction at atmospheric pressure and $0$C$.$ The mole fraction of CO$2$ at point A is $0\mathrm{.}2$; at point B$,3$ m away, in the direction of diffusion, it is $0\mathrm{.}02.$ The concentration gradient is constant over this distance. Diffusivity of CO$2$ in N$2$ under the given conditions is $0\mathrm{.}144$ cm$2/$s$.$ The gas phase as a whole is stationary; i$.$e$.,$ N$2$ is diffusing at the same rate as the CO$2,$ but in the opposite direction.

a$)$ What is the molal flux of CO$2$ in kgmoles$/$m$2.$h$?$

b$)$ What is the net mass flux in kg$/$m$2.$h$?$

Can you provide a detailed step$-$by$-$step solution using mass transfer formulas?