In a certain mathematics competition, there were 20 questions in total, 5 points were awarded for each correct question, 2 points were deducted for not doing or doing wrong, Xiao Cong scored 72 points, how many questions did he get wrong.
某次数学竞赛，共有20道题，每道题做对得5分，没做或做错都要倒扣2分，小聪得了72分，他做错了多少道题．
<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>

<result>4</result>