A jeweler has a fixed amount of gold to make bracelets and necklaces. The amount of
 gold in each bracelet is 6 grams and the amount of gold in each necklace is 20 grams.
 How much gold, in grams, would it take to make 7 bracelets and 9 necklaces? How
 much gold, in grams, would it take to make b bracelets and n necklaces?