The price of a hardcover book is 23 yuan, the book itself is 17 yuan more expensive than the book cover, how much is the book cover.
一本精装书的定价是23元，书本身比书皮贵17元，书皮要多少元．
<gadget id="calculator">23 + 17</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">23 - 20</gadget>
<output>3</output>

<result>3</result>