There are 30 questions in a certain mathematics competition. The scoring standard is: 5 points for each correct question, and 2 points for each wrong answer or failure to answer a question. Wang Cong participated in this competition and scored 115 points. How many questions did he get right?
某次数学竞赛共30道题，评分标准是：每做对一题得5分，每做错或不做一题扣2分．王聪参加了这次竞赛，得了115分．他做对了几道题？
<gadget id="calculator">30 * 5</gadget>
<output>150</output>

<gadget id="calculator">150 - 115</gadget>
<output>35</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">35 / 7</gadget>
<output>5</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<result>25</result>