Figure4-6The Supply Curve for Used Textbooks The supply curve illustrates seller’s cost, the lowest price at which a potential seller is willing to sell the good, and the quantity supplied at that price. Each of the five students has one used book to sell and each has a different cost, as indicated in the accompanying table. At a price of $5 the quantity supplied is one (Andrew), at $15 it is two (Andrew and Bahira), and so on until you reach $45, the price at which all five students are willing to sell.