Answer:
Susan is correct. If you divide the unit price (the price of each individual soda) by the number of people, you will get the total cost of the soda. Or in other words, how much money you're putting down to buy this soda for X amount of people. John is incorrect because by dividing the cost of a 12 pack soda by the number of sodas, he is determining the cost of each individual soda, not the total cost.