In the third grade, 16 people participated in the extracurricular group, among which 10 people participated in the art class, and 9 people participated in the dance class. How many people participated in both classes?
三年级参加课外小组的有16人，其中参加美术班的有10人，参加舞蹈班的有9人，两个班都参加的有多少人．
<gadget id="calculator">9 - 16</gadget>
<output>-7</output>

<gadget id="calculator">10 + (-7)</gadget>
<output>3</output>

<result>3</result>