There are 15 questions in the mathematics competition. It is stipulated that each correct question will get 8 points, and each wrong answer will deduct 4 points. Xiaohua will get 72 points in total. How many questions did he get wrong.
数学竞赛题共15道，规定每做对一题得8分，每做错一题倒扣4分，小华共得72分．他做错了多少道题．
<gadget id="calculator">8 * 15</gadget>
<output>120</output>

<gadget id="calculator">120 - 72</gadget>
<output>48</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">48 / 12</gadget>
<output>4</output>

<result>4</result>