Zhang Hua took the Gaobo Education three-subject league math test. There were 15 questions in total, 8 points for each pair of questions, and 4 points deducted for not answering or wrong one question. Zhang Hua scored a total of 84 points. How many questions did Zhang Hua get right?
张华参加高博教育三科联赛数学考试，一共15道题，每对一题得8分，不答或错一道题倒扣4分，张华一共得了84分．请问张华做对了多少道题？
<gadget id="calculator">15 * 8</gadget>
<output>120</output>

<gadget id="calculator">120 - 84</gadget>
<output>36</output>

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

<gadget id="calculator">36 / 12</gadget>
<output>3</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>