Seventy five years ago pharmacists weighed medicine on balances like the ones you have been using. The mass pieces were very expensive, so a pharmacist would buy as few mass pieces as possible. If a pharmacist had 1-g, 3-g, and 9-g mass pieces, he or she could weight out any number of grams from 1 g to 13 g. Show how could measure all of the masses from 1 g to 13 g using only the three mass pieces given?