Answer:
b. 3 McBurgers and 2 cans of Alpo
Step-by-step explanation:
If the goal is to maximize utility, Ms. Tightwad should look into purchasing the combination that yields the highest utility.
a. 4 McBurgers, 0 Alpo cans:

b. 3 McBurgers, 2 Alpo cans:

c. 2 McBurgers, 4 Alpo cans:

d. 1 McBurger, 6 Alpo cans (assume marginal utility stays constant after the 4th can):

Since option b. yields the highest utility, she should buy 3 McBurgers and 2 cans of Alpo