Ok, so
We want to find the unit cost of each package to find the better buy.
We know that $4.99 is the cost for a case of 24 twelve-oz cans.
If we divide:
Then, the cost for each can in the option a, is $0.20791.
Now, we know that $5.00 is the cost for a 12-pack of 8-oz cans.
If we divide:
Then, the cost for each can in the option b, is $0.4166
Notice that in the option a, we know that there are cans with 12-oz.
The unit price, can be found if we divide the price of each can, by its capacity.
In the option A, we obtain:
This is, 0.017 dollars per oz.
In the option b, we know that there are cans with 8-oz.
If we calculate the unit price, we got that:
This is, 0.052 dollars per oz.
If we compare, we clearly notice that the best option to buy is a, because the units (dollars / oz) indicates us that the price for each oz, is cheaper, with 0.017 dollars / oz.