This is about positive externality. From the information given (in the attached),
In order to ensure that the market produces at optimal efficiency, the government must Impose corrective subsidies.
Subsidy = 11-7
= $4
As a result of the positive externality of the market produced the optimal amount. (Option B)
A positive externality occurs when a benefit is passed on to a third party.
Negative externalities can be discouraged by charging goods and services that cause spillover costs.
Learn more about positive externality at;
https://brainly.com/question/477170
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