There are 28 people in Class 5 and 3 who have subscribed to "Primary School Students' World", and 20 people have subscribed to "China Youth Daily". There are 42 students in the class, and each of them has subscribed to at least one of the two publications. How many people are there.
五3班有28人订立《小学生天地》，20人订了《中国少年报》，班上共有42名学生，每人至少订立了两种刊物中的一种，那么，两种书都订了的有多少人．
<gadget id="calculator">20 - 42</gadget>
<output>-22</output>

<gadget id="calculator">28 + (-22)</gadget>
<output>6</output>

<result>6</result>