Jared and Missy are buying refreshments for their class party. Jared is buying a variety case of juice for $20. Missy is buying cartons of grape juice for $2 and cartons of apple juice for $3. Evaluate the expression 2g+3a when g=4 and a=8 to find the cost of buying 4 cartons of grape juice and 8 cartons of apple juice. What is the difference in price Missy and Jared paid? Show your work.