The surface tension of water with a mole fraction of $0\mathrm{.}001,0\mathrm{.}002,0\mathrm{.}003,$dots,$0\mathrm{.}007$ of n$-$propanol is $67\mathrm{.}4,64\mathrm{.}4,61\mathrm{.}9,59\mathrm{.}7,57\mathrm{.}7,55\mathrm{.}8,$ and $54\mathrm{.}1\frac{N}{m}$ at $25C,$ respectively. Estimate the surface excess of propanol at mole fractions of $0\mathrm{.}002,0\mathrm{.}004,$ and $0\mathrm{.}006.$