Yeah, lets assume that the conditions raised in that block of text you copied from your text book are all satisfied. If you feel like it, paste it in you answer, if you expect your teacher is trying to trick you. Can you break your given question into what you know, and what you don't? Can you plug into the Beer's Law equation, likely found in your text, nearby your quoted block of text, or on ARGOS++:'s website? And can you work backward from what you know, to what you need to know?