Official Explanation
Let b = the marked price of the book. The sales tax is 9% of the book’s marked price, so tax = .09 b. Then the cost of the book plus tax is given by \(1b + .09b,\) which equals 1.09b. Since John received change for his $20 bill, and since the change was less than $5, he must have spent between $15 and $20. Then \($15 < 1.09b < $20.\) Divide all three parts of this inequality by 1.09 to obtain $13.76 < b < $18.35. This result implies both (A) and (B), because b is certainly greater than $13.50 but less than $18.50. Choice (C) is not true, because if the marked price were $18, for example, then the sales tax would have been .09 × $18 = $1.62, which is greater than $1.50, while the total price remains low enough, $19.62, to leave John change, as required.
Answer: A,B