6.3 Ms. Sarah Traveler does not own a car and travels only by bus, train, or plane. Her utility function is given by utility

b. p, where each letter stands for miles traveled by a specific mode. Suppose that the ratio of the price of train travel to that of bus travel (P./P) never changes.

a. How might one define a composite commodity for ground transportation?

b. Phrase Sarah's optimization problem as one of choosing between ground (g) and air (p) transportation.

c. What are Sarah's demand functions for g and p?

d. Once Sarah decides how much to spend on g, how will she allocate those expenditures between b and t