Teacher Li plans to arrange several classrooms for the students who participate in the winter camp for mathematics lovers. After the campers arrived, Teacher Li found that according to the original plan, the number of campers living in each dormitory was not all the same. He calculated that if 2 dormitories are added, each dormitory will accommodate exactly 6 people; if 2 dormitories are reduced, each dormitory will accommodate exactly 9 people. How many campers are participating in the winter camp?
李老师计划为参加数学爱好者冬令营的同学安排若干件教室．营员们到来之后，李老师发现，按照原先的计划，每间宿舍住的营员人数不全是同样多．他一计算，如果增加2间宿舍，每间宿舍恰好住6人；如果减少2间宿舍，每间宿舍恰好住9人．参加冬令营的营员共有多少人．
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 + 2</gadget>
<output>12</output>

<gadget id="calculator">12 * 6</gadget>
<output>72</output>

<result>72</result>