There are 20 questions in a mathematics competition. You get 5 points for a correct question, and 2 points for a wrong question. Liu Dong scored 72 points in the test. Do you know how many questions Liu Dong got right?
一次数学竞赛共有20道题．做对一道题得5分，做错一题倒扣2分，刘冬考了72分，你知道刘冬做对多少道题．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 72</gadget>
<output>28</output>

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

<gadget id="calculator">28 / 7</gadget>
<output>4</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>