Final answer:
Justin should charge his friend $1.60 per pack of baseball cards.
Step-by-step explanation:
To find out how much Justin should charge for the 10 packs of baseball cards, we need to first calculate the discounted price per pack. We can do this by dividing the total cost of the 40 packs by 40. $64/40 = $1.60 per pack
Since Justin wants to sell the packs at cost, he should charge his friend the same amount he paid per pack, which is $1.60