The important role of a government is to provide public goods and services. The example of public goods and services provided by a government are public transport, road maintenance, security to the people.
Economists consider public transport as a public good because it is difficult to exclude the people from the use of it.
Security provided by a local government is also considered as public good because it benefits to all the people. People cannot be excluded from using the road, thus, it is considered as a public good.
If relatively more inputs are required to produce a pound of coffee, then it would reduce the allocated resources to harvest tea. A change in the production technique of coffee affects the production of tea.
Relatively more resources have to be used for harvesting a pound of coffee. This will hamper the overall production of coffee and tea altogether.
The price of coffee is likely to increase in the market due to a new disease that requires to relatively more resources. The price of tae is likely to remain same considering no changes in the cost of production.
The opportunity cost to the society of a 100-mile truck trip is equals to value of the availability of goods and services that are transported by 100-miles trip.
The price of gasoline is not sufficient to represent the opportunity cost because the clean environment relinquishes due to 100-miles truck trip.
Truck trips lead to pollute the environment. So, the forgone cost of clean environment is required to consider while measuring the opportunity cost to the society of a 100-mile truck trip.