There are 15 questions in one test paper, 6 points for answering one question correctly, 4 points for one wrong answer, and 0 points for Xiaoming who answered all the questions, so how many questions did he answer correctly in total?
一张试卷共有15道题，答对一道题得6分，答错一道题扣4分，小明答完了全部的题目却得了0分，那么，他一共答对了多少道题．
<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">90 - 0</gadget>
<output>90</output>

<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<gadget id="calculator">90 / 10</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>