Harry Potter participated in the mathematics competition, and he scored 68 points in total. The scoring standard is: 20 points for each correct question, and 6 points deducted for each wrong question. It is known that the number of correct questions is twice that of the wrong ones, and he has done all the questions. Excuse me, how many questions are there in this set of test papers? (solution with equation)
哈利•波特参加数学竞赛，他一共得了68分，评分标准是：每对一道题得20分，每错一道题倒扣6分．已知他做对题的数量是做错题的2倍，并且所有的题他都做了，请问，这套试卷有多少道题？(用方程解答)
<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 - 6</gadget>
<output>34</output>

<gadget id="calculator">68 / 34</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<result>6</result>