A $2\mathrm{.}0\%$ by weight aqueous surfactant solution has a surface tension of $69\mathrm{.}0$ dyn$/$cm at $20$C$.($a$)$ Calculate $,$ the area of surface containing one molecule. State any assumptions that must be made to make the calculation from the data. $($b$)$ The additional information is now supplied that a $2\mathrm{.}2\%$ solution has a surface tension of $68\mathrm{.}8$ dyn$/$cm$.$ If the surface$-$adsorbed film obeys the equation of state $,$ calculate from the combined data a value of $0,$ the actual area of a molecule.