There are 25 students in class 303, and many students participated in extracurricular groups. There are 12 people in the music group, 10 people in the art group, and 6 people in neither group. How many students participated in both the music group and the art group?
303班有25人，许多同学参加了课外小组．参加音乐组的有12人，参加美术组的有10人，两个组都没参加的有6人．既参加音乐组又参加美术组的有多少？
<gadget id="calculator">25 - 6</gadget>
<output>19</output>

<gadget id="calculator">10 - 19</gadget>
<output>-9</output>

<gadget id="calculator">12 + (-9)</gadget>
<output>3</output>

<result>3</result>