A tray tower is to be designed to absorb SO$2$ from an air stream by using pure water at $293$ K $(68\backslash$deg F$).$ The entering gas contains $20$ mol $\%$ SO$2$ and that leaving $2$ mol $\%$ at a total pressure of $101\mathrm{.}3$ kPa. The inert air flow rate is $150$ kg air$/$h$.$m$^2$ and the entering water low rate is $6000$ kg water$/$h$.$m$^2.$ Assuming an overall tray efficiency of $25\%,$ how many theoretical trays and actual trays are needed? Assume that the tower operates at $293$ K $(20\backslash$deg C$).$