Xiao Ming participates in a math competition, with a total of 20 questions, 5 points for a correct answer, 2 points deducted for a wrong question, and 72 points for the final question. How many questions did Xiao Ming get wrong?
小明参加数学比赛，一共20道题，做对一题得5分，做错一题倒扣2分，结题小明得了72分，小明做错了多少题．
<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>

<result>4</result>