the willingness to pay of the marginal buyer, the buyer who would leave the market
first if the price were any higher. At a quantity of 4 albums, for instance, the demand
curve has a height of $50, the price that Ringo (the marginal buyer) is willing
to pay for an album. At a quantity of 3 albums, the demand curve has a height
of $70, the price that George (who is now the marginal buyer) is willing to pay.