Stan and Francine want to make perfume. In order to get the right balance of ingredients for their tatses they bought 2 ounces of rose oil at $3.72 per ounce, 4 ounces of ginger essence for $4.33 per ounce, and 4 ounces of black currant essence for $4.15 per ounce. Determine the cost per ounce of the perfume.