The Market Supply and Demand Functions for a Good Traded $$Q D = 40 - 2 P \text { and } Q S = 15 + 3 P$$

Essay

The market supply and demand functions for a good traded on a perfectly competitive market are:
$$Q D = 40 - 2 P \text { and } Q S = 15 + 3 P$$ (i)What is the equilibrium price and quantity on this market?
(ii)If the production of each unit of this good gives rise to a social cost of $1, what is the socially optimal equilibrium quantity and price? Assume that producers pay a tax of $1 per unit.
(iii)If the production of each unit of this good gives rise to a social benefit of $5, what is the socially optimal equilibrium quantity and price? Assume that producers receive a subsidy of $5 per unit.