Ok, so:
We know that Walter could buy 2 bags for $12 each, 3 bags for $8 each, and 4 bags for $6 each.
Let me draw a table to see the situation clearly.
B is bag, and P is price.
We can clearly see that if the number of bags increases, the price is decreasing. So, we know that this is an inverse variation. Now, what option would be the most appropiate?
If the number of bags is "x", and "y" is the price, we notice that the product x*y is always 24. And from the table, we know that this is an inverse variation.
So the answer, is B.