A total of 45 people from class 3 and 8 participated in extracurricular interest groups, including 28 people in the art interest group and 25 people in the dance interest group. How many people participated in both interest groups?
三8班共有45人参加了课外兴趣小组，其中参加美术兴趣小组的有28人，参加舞蹈兴趣小组的有25人，请问两种兴趣小组都参加的有多少人？
<gadget id="calculator">25 - 45</gadget>
<output>-20</output>

<gadget id="calculator">28 + (-20)</gadget>
<output>8</output>

<result>8</result>