Suppose a consumer has well-behaved preferences over junk food, J, and other food, F. Suppose that at the current level of consumption, we have MRS_JF = 4. Suppose:
a) The consumer is indifferent between consuming junk food and other food.
b) The consumer is willing to trade 4 units of other food for 1 unit of junk food.
c) The consumer is willing to trade 4 units of junk food for 1 unit of other food.
d) The consumer's preferences are not well-defined.