I need a detailed solution. Because of the brevity, I don't understand

Example 2: A soluble gas is to be absorbed from an air - gas in a packed tower using solute free liquid. The equilibrium relation is y=mx. (1)Show that the number of overall transfer unit is given by: NOG=11ln[(1)y2y1+]where=mLsGs (2) If 99% of the solute is to be recovered using a liquid rate of 1.75 times the minimum and the height of the transfer unit is 1.0m. What packed height is required? Sol: (1) The derivation is above in lucture (2) y2=(1recovery)y1=(10.99)y1=0.01y1(GsLs)min=m(1y1y2)=m(1y10.01y1)=0.99m(GsLs)ac=1.75(GsLs)min=1.750.99m=1.7325m=mLsGs=1.7325mm=0.577NOG=11ln[(1)y2y1+]NOG=10.5771ln[(10.577)0.01y1y1+0.577]=8.88Z=HOG.NOG=18.88=8.88m