Imagine a market where there is a negative externality in consumption. The private inverse demand function for the good is:

D_private: P_D = 18 - 2Q_D.

The social inverse demand function that incorporates the negative externality is:

D_social: P_D = 12 - 2Q_D.

The social (and private) inverse supply function is:

S_social: P_S = 3 + Q_S.

A ______ would eliminate the deadweight loss from the externality, which equals _____.

Select one:

a.$3 per unit tax; $12.

b.$6 per unit tax; $6.

c.$3 per unit subsidy; $12.

d.$6 per unit tax; $3.

e.$6 per unit subsidy; $6