To find the benefit of an additional unit of a public good, we sum the individual demand curves:

• A. Horizontally
• B. Vertically
• C. Diagonally
• D. None of the above

Answer: (B)

Verified step by step guidance

1. Understand the nature of public goods: Public goods are non-excludable and non-rivalrous, meaning that one person's consumption of the good does not reduce its availability to others.
2. Recognize that the benefit of a public good is the sum of the benefits to all individuals in the society. This is because everyone can consume the public good simultaneously.
3. Identify that individual demand curves for public goods represent the marginal benefit each individual receives from an additional unit of the good.
4. To find the total benefit of an additional unit of a public good, sum the individual marginal benefits. This is done by adding the individual demand curves vertically, as each individual's willingness to pay is added at each quantity level.
5. Conclude that the correct method to find the benefit of an additional unit of a public good is to sum the individual demand curves vertically, reflecting the total willingness to pay for each additional unit of the public good.