Pure gas A is diffusing from a point $1$ at a partial pressure of $1$

atm. to a point $2$ at a distance $1\mathrm{.}0$ mm away. At point $2$ it undergoes instantaneous chemical reaction at the catalytic surface as A$-3$B Gas B diffusing back at the steady state. The total pressure is $1$ atm, and temperature is $27$C$.$ The molecular diffusivity, DAB $1\mathrm{.}5$x$10-5$ m$2/$s$.$ Calculate molar flux of A $($kg mol$/$m$2$ s$)$ at steady state.