The better deal is Cheerios because
If you take the ounces for each (17 & 13)
And divide them by the price ($3.89 & 2.89)
It would give you the amount 1 ounce would be (aka the constant) and the constant for Cheerios is 4.3701 where as the constant for Apple Jacks is 4.4981. Therefore, Cheerios is the better deal cause you get more.