EXAMPLE $18\mathrm{.}5.$ Water containing $6$ ppm trichloroethylene $($TCE$)$ is to be purified by stripping with air at $20^($@$)$C$.$ The product must contain less than $4\mathrm{.}5$ppb TCE to meet emission standards. Calculate the minimum air rate in standard cubic meters of air per cubic meter of water and the number of transfer units if the air rate is $1\mathrm{.}5$ to $5$ times the minimum value. Solution. Henry's law coefficient for TCE in water $^($n$1)$ at $20^($@$)$C is $0\mathrm{.}0075$m$^(3)*$atm$//$mol$.$ This can be converted to the slope of the equilibrium line in mole$-$fraction units as follows, since P$=1$atm and $1$m$^(3)$ of liquid weighs $10^(6)$g :

I don't want to use concentration to solve it as shown in the textbook.

I want to solve the problem in fractions

I know the answer, but I don't know the answer.

xa$-$xb$=8\mathrm{.}22$X$10^-7$

xb$*-$xb$=6\mathrm{.}16$X$10^-10$

xa$*-$xa$=2\mathrm{.}73$X$10-7$

Tell me how to get xa$,$ xb$,$ xa$*,$ xb$*$