In 1984, a 12-ounce box of cold cereal cost $0.89. in 2008, an 18-ounce box of the same cereal sold for $3.29. how much more was the cost of the cereal per ounce in 2008 than in 1984? explain

Well, we can just divide them.

0.89 / 12 is approximately $0.07

3.29 / 18 is approximately $0.18

0.18 - 0.07 = $0.11

So the cost of cereal in 2008 is 11 cents more per ounce than the cereal in 1984.

Firstly we need to find out how much is worth 1 ounce of cold cereals both in 1984 and 2008. Do do that we may just divide both numbers by 12:

0.89 ÷ 12 ≈ 0.07 (I rounded it to the neaerest cent as we're talking about money anyway)
3.29 ÷ 18 ≈ 0.18

So in 1984 one ounce costed $0.07, while in 2008 it costed $0.18.

To find out how much more was it in 2008, we just need to do the substraction:

$0.18 - $0.07 = $0.11

The cost of the cereals per ounce was bigger in 2008 than in 1984 by $0.11.