Do 20 questions, get 5 points for one answer, and deduct 2 points for one wrong question or not doing it. Xiaoyun scored 65 points, how many questions did she get right.
做20道题，对一道得5分，错一题或不做扣2分．小云得分65分，她做对多少题．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 65</gadget>
<output>35</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">35 / 7</gadget>
<output>5</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<result>15</result>