$[50]$ The surface tension of an aqueous solution varies with the concentration of sodium dodecylsulfate to pure water according to the equation $(\frac{mJ}{m^2})=(72-6000C)(1-\frac{T}{647(K)})($provided that $C$ is less than $0\mathrm{.}05M,T$ is temperature $(K)).$

A$)[20]$ For a porous solid with $10nm$ pores, estimate the humidity of $0\mathrm{.}5mM$ sodium dodecylsultate solution with $V_m=18c{m}^3$ at $298K.$

B$)[30]$ Calculate the area of surface containing one molecule and the surface excess with addition of $1\mathrm{.}0mM$ sodium dodycylsulfate at $298K.$