The students in class 31 subscribed to three newspapers, and each student subscribed to two. Among them, "Primary School Students' Mathematics Newspaper" subscribed to 36 copies, "Chinese Newspaper" subscribed to 24 copies, and "China Children's Daily" subscribed to 30 copies. How many people are subscribed to both "Primary School Students' Mathematics Journal" and "Chinese Newspaper".
三1班同学订阅了三种报纸，每位同学都订阅了两种，其中《小学生数学报》订了36份，《语文报》订了24份，《中国少年儿童报》订了30份，《小学生数学报》和《语文报》都订的有多少人．
<gadget id="calculator">24 - 30</gadget>
<output>-6</output>

<gadget id="calculator">36 + (-6)</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>