Final answer:
The production possibilities frontier (PPF) for the United States is 80 shirts.
Step-by-step explanation:
The production possibilities frontier (PPF) for the United States can be graphed using the blue line (circle symbol). The PPF shows the maximum amount that the United States can produce given its limited resources and technology. In this case, the United States can produce 80 shirts or 20 computers. Therefore, the production possibilities frontier for the United States is 1) 80 shirts.