Final answer:
The opportunity cost for producing additional goods cannot be determined without specific trade-off data, which is usually shown on a Production Possibility Frontier reflecting the trade-off between two different goods. The law of increasing opportunity cost illustrates that more of one product can only be made at a higher opportunity cost of the other.
Step-by-step explanation:
Understanding the opportunity cost is essential in analyzing Production Possibility Frontiers (PPFs), which show the different quantities of two goods that a firm can produce using the same finite resources. The opportunity cost represents the number of units of one good that must be forgone to produce an additional unit of another good. In your given scenario, the student's question, 'What is the opportunity cost for making 4,000 additional briefcases if the company is currently at point D on the PPC?', cannot be directly answered without specific data showing the trade-off between briefcases and the other goods mentioned (pairs of shoes, hats, belts, gloves). Typically, such data can be reflected via a table or graph associated with the PPC, showing how output of one good decreases as the output of another increases.
The law of increasing opportunity cost states that as more units of one good are produced, the opportunity cost in terms of forgone units of the other good will rise. This is depicted in the PPC as a concave curve, where moving from one point to another results in increasing trade-offs. In the examples provided, different plants have different opportunity costs for producing additional units, and the firm would allocate resources to plants with the lowest opportunity costs first.