The price of a hardcover book is 13 yuan. The book itself is 11 yuan more expensive than the book cover, how much is the book.
一本精装书的定价是13元．书本身比书皮贵11元，书多少元．
<gadget id="calculator">13 + 11</gadget>
<output>24</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<result>12</result>