Answer: They would have to borrow 7 DVDs. The total cost of either plan would be $15.
Explanation:
The first fee is $8, with an added $1 for every DVD rented. The second fee is $15 for unlimited. For the two plans to each cost the same for a month, a person using the first fee would need to borrow 7 DVDs. That would be $7. Add that to $8 & you get $15.