What would the Welfare Loss be due to Ignoring Negative Production Externalities?

-Welfare Loss is the Loss to Society by Ignoring Externalities -For this case, The Welfare Loss would be a Tringle, with its Points being: -A: Equilibrium Point [Free Market] -B: Point on MSC that is Directly above the Equilibrium Point [A] [The External Cost] -C: Socially Optimal Point