There are 42 people in class 3 and 2, 24 people like rope skipping, 28 people like running, how many people like both sports.
三2班有42人，喜欢跳绳的有24人，喜欢跑步的有28人，两种运动都喜欢的有多少人．
<gadget id="calculator">24 - 42</gadget>
<output>-18</output>

<gadget id="calculator">28 + (-18)</gadget>
<output>10</output>

<result>10</result>