I need help with this question please. The answer is not 60.00 nor 80.00. Can you please help me understand this question more please. Thank you.

Consider the file named Public Goods Graphs. It shows the marginal private benefits (MPB) derived by three citizens from different units of a public good such as a fire station, another military base, or a new freeway. It also shows the marginal social costs of building these goods. Suppose that when the government employees survey the citizens about their preferences for the public good, every citizen understate his or her marginal private benefit for every unit of the good by $20. In that case, the survey results would mistakenly indicate that the allocationy efficient number of the public good is Use our general rounding rule.