A set of "Encyclopedia" consists of three copies, priced at 45.9 yuan, two of which are priced at 16.5 yuan, how much is the price of the third book?
一套《百科全书》共三本，售价45.9元，其中两本的价格都是16.5元，第三本书售价多少钱？
<gadget id="calculator">16.5 * 2</gadget>
<output>33</output>

<gadget id="calculator">45.9 - 33</gadget>
<output>12.9</output>

<result>12.9</result>