How might government correct this divergence

Question

What divergences arise between equilibrium and an efficient output spillover benefits are present?  How might government correct this divergence?

Answer 1

When spillover benefits are present, the equilibrium output will be smaller than the efficient output because the consumer is willing to pay a price equal to the consumer’s individual marginal benefit, but no more.  Since social benefits exist in addition to the private benefit, the government must either aid the producer to encourage more output or engage in its own production of the item with the spillover benefits.