Choice C is the correct answer. Let $b$ be the number of books.

Store 1: $C_1 = 15b + 8$Store 2: $C_2 = 18b$

Set equal: $15b + 8 = 18b$$8 = 3b$$b = \frac{8}{3} \approx 2.67$

Since we need whole books, round up to 3.

• 2 books: Store 1 = $38, Store 2 =$36 (not equal)
• 3 books: Store 1 = $53, Store 2 =$54 (close)

💡 Strategic Tip: Break-even problems compare two linear cost models.

Choice A is incorrect because costs are $24 vs$18.

Choice B is incorrect because costs are $39 vs$36.

Choice D is incorrect because costs are $69 vs$72.