There are 5 questions in a certain knowledge contest, and there are 52 students in the class, and one point is awarded for each correct answer. It is known that the whole class has a total of 181 points. It is known that each person has at least 1 point, and there are 7 people who get 1 point, as many people get 2 points as 3 points, and 6 people get 5 points, how many people get 4 points?
某次知识竞赛共5道题，全班52人，答对一题得1分．已知全班共得181分．已知每人至少得1分，且得1分的有7人，得2分和得3分的人一样多，得5分的人有6人，则得4分的有多少人．
<gadget id="calculator">4 * 39</gadget>
<output>156</output>

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

<gadget id="calculator">30 - 181</gadget>
<output>-151</output>

<gadget id="calculator">7 + 156 + (-151)</gadget>
<output>12</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 - 2 - 3</gadget>
<output>3</output>

<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">39 - 8</gadget>
<output>31</output>

<result>31</result>