There is a class of students who go boating in the park. They have already rented several boats in advance. Now if one more boat is added, each boat can take exactly 6 people; How many people are there in this class?
有一个班的同学到公园去划船，他们已提前租好了若干条船，现在如果增加一条船，正好每条船坐6人；如果减少一条船，正好每条船坐9人．这个班共有多少人？
<gadget id="calculator">6 + 9</gadget>
<output>15</output>

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

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

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

<gadget id="calculator">6 * 6</gadget>
<output>36</output>

<result>36</result>