I'm not quite sure what you're asking, but I'll try to help anyway!
So if I'm not misinterpreting the question, you're asking how much one pack of gum would cost, and the packs are in a case which is in the deal of the 3 for $54
Then lets get started!
If you pay $54 for 3 cases, then how much would 1 case of gum be?
$54 / 3 = $18 per case
Then we consider the packs in a case.
Each one has 24 packs and you want to find how much 1 pack would cost. So do the same thing as before!
Cost of one case / number of packs = $18 / 24 =$3/4 = 75 cents.