Lady Edith bought several necklaces at the jewelry store, and each necklace cost 16 dollars. Lady Mary
also purchased several necklaces, at a cost of $20 each. If the ratio of the number of necklaces Lady Edith
purchased to the number of necklaces Lady Mary purchased is 3 to 2, what is the average cost of the
necklaces purchased by Lady Edith and Lady Mary?