quick-answer game stipulates that 15 points will be awarded for a correct answer, and 8 points will be deducted for a wrong answer. Xiaohua answered 18 questions quickly; the final score is 40 points, how many questions she answered correctly.
一次抢答游戏规定，答对一题加15分，答错一题要扣8分，小华抢答了18题；最后得分是40分，她答对了多少题．
<gadget id="calculator">15 * 18</gadget>
<output>270</output>

<gadget id="calculator">270 - 40</gadget>
<output>230</output>

<gadget id="calculator">15 + 8</gadget>
<output>23</output>

<gadget id="calculator">230 / 23</gadget>
<output>10</output>

<gadget id="calculator">18 - 10</gadget>
<output>8</output>

<result>8</result>