Doudou participated in a math competition. There are 20 questions in total, 5 points are given for each correct answer, and 1 point is deducted for each wrong answer. Doudou completed all the answers and scored 70 points in total. How many questions did Doudou answer correctly?
豆豆同学参加一次数学竞赛．试题共20道，规定答对一道得5分，答错一道扣1分．豆豆全部完成了答题，共得了70分．豆豆答对了多少道题？
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 70</gadget>
<output>30</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<result>15</result>