how externalities may prevent market equilibrium, economics homework help

I need an APA format of an intro, completion of these 2 points, and a conclusion. The 2 points need one peer reviewed source in the paragraph for each point and I also need the actual citation for the reference page.
  • Discuss how externalities may prevent market equilibrium and the various governments policies used to remedy the inefficiencies in markets caused by externalities.
  • Analyze the difference between the efficiency of a tax system and the equity of a tax system as it refers to the costs imposed on taxpayers using the benefits principles.