142. Solving a chemistry problem

10.17. Calculate the average value of the absorption coefficient during the passage of light rays (wavelength 600 · 10–3 m) through a layer with a thickness l of a sol of mastic of various concentrations. The percentage of transmitted IP rays is given from the experimental data of Theorell.
Concentration C,% 0.6 0.20 0.10 0.06 0.02 0.01
l103, m 2.5 2.5 5.0 20.0 20.0 30.0
IP,% 2.7 63.9 65.8 37.1 70.1 77.8