In its efforts toward sustainability, an American university campus is replacing paper towel dispensers in restrooms with electric hand dryers based on air drying. Another hand-drying system popular in Europe uses a roll of cloth towel. Many restrooms in other parts of the world lack a hand-drying system, so people carry their own cloth handkerchief for drying their hands. What information will you need to determine the functional unit for comparing these four systems in terms of their life cycle environmental impact? On the basis of your own research about the functioning of these systems and their typical use, determine the functional unit for each system.