Q$4.(35)$ A tray tower is to be used to absorb $99\%$ of the ammonia from an entering gas stream $($air $+$ ammonia$)$ containing $30$mol$\%$ ammonia at $30C$ and $1$atm.

a$)$ What is the minimum flow L$\text{'}?$

b$)$ Calculate the number of theoretical trays needed using $1\mathrm{.}5$ times factor the minimum plot the equilibrium and operating lines. Assume the entering gas flow rate is $1$mol. The vapor$-$liquid equilibria can be represented by $Y_A=1\mathrm{.}74x_A.$ Draw the operating$-$line by obtaining four points.