There are 45 people in class 3 and 1. Everyone participates in calligraphy and Latin dance activities. Among them, 28 people participate in calligraphy activities, and 24 people participate in Latin dance activities. How many people participate in calligraphy and Latin dance activities at the same time?
三1班有45人，人人参加书法、拉丁舞兴趣活动，其中参加书法活动的有28人，参加拉丁舞活动的有24人，同时参加书法、拉丁舞活动的有几人？
<gadget id="calculator">24 - 45</gadget>
<output>-21</output>

<gadget id="calculator">28 + (-21)</gadget>
<output>7</output>

<result>7</result>