can u explain both of this question.

Suppose supply is given by the equation Ps=2+Qs and demand is given by the equation Pd=50-2Qd. Price is in dollar; quantity is in thousands unit. Assuming the current level of imports is 12,000units. If a tariff of $4 is imposed, then increase in surplus compared to no trade will be

A:$48,000 from imports of 12,000units

B:$12,000 from imports of 6000 units

C:36,000,6000

D36,000,12,000

Factories cutting trees for wood creates a negative externality of $50 per tree. The government imposes a $50 tax on each tree cut. What is the relationship between the after tax equilibrium quantity and the socially optimal quantity of trees to be cut?

A:the after tax equilibrium quantity is greater than the socially optimal quantity.

B:The after tax equilibrium quantity is less than the socially optimal quantity

C:There is not enough infos to answer the question

D:they are equal