This is such a stupid problem, but my brain is completely locked when I try to figure out the rationale for why it is A or B.Ait is 20%, because 1 cm is 50% of 2 cm and 20% is 50% of 40%. orBit is 1-0.6^0.5=0.22.. ~22% because the 2 cm thick lets 60% in and the 1 cm is half of it, so that type of equation would seem to make some sense.

Thanks for the help.