There are 42 students in a class, 30 students participate in the sports representative team, and 25 students participate in the art representative team, and each of them participates in at least one team. How many students in this class participate in both teams?
一个班有学生42人，参加体育代表队的有30人，参加文艺代表队的有25人，并且每个人至少参加了一个队，这个班两个队都参加的有几个人？
<gadget id="calculator">25 - 42</gadget>
<output>-17</output>

<gadget id="calculator">30 + (-17)</gadget>
<output>13</output>

<result>13</result>