Answer:
362
Explanation:
The total of costs for printing 500 books is ...
$250 +500($3) = $1750
The profit is the difference between revenue and cost.
revenue -cost = profit
9b -1750 > 1500
9b > 3250
b > 3250/9 =361 1/9
The number of books they need to sell is at least 362.
__
Additional comment
If the books could be printed one at a time, then the 9-3 = $6 contribution margin of each book would require sale of 250/6 = 41 2/3 books to cover the printer setup charge and 1500/6 = 250 books to achieve the desired profit, for a total of 292 books. However, the books were printed in a batch of 500, so the cost of printing those extra books must also be covered. That is why we need to sell 362 books for a profit of at least $1500.