Textbook Problem

Which of the following might lead to an increase in the equilibrium price of jelly and a decrease in the equilibrium quantity of jelly sold?

a. an increase in the price of peanut better, a complement to jelly

b. an increase in the price of Marshmallow Fluff, a substitute for jelly

c. an increase in the price of grapes, an input into jelly

d. an increase in consumers’ incomes, as long as jelly is a normal good