Question

A package of 8 count batteries costs $6.16. A package of 20-count AA BATTERIES COSTS $15.20.

Answer 1

The unit price of the 20 pack is $0.79 and the unit price for the 8 pack is $0.80.

Simply Take the price of the pack of batteries divided by the number within the pack.
$6.40 / 8 == $0.80
$15.80 / 20 == $0.79