The equilibrium price and quantity within a market for a good can be found at the intersection of the supply and demand curves. Therefore, we need to use a mathematical method to find the P and Q by equating the two expressions. 100 - P = 40 + 2P 100 - 40 = 2P + P 60 = 3P P = 20 therefore Q = 100 - 20 = 80 therefore the equilibrium price for this good is 20 at 80 units sold.