There are 16 students in Class 1 of the third grade who ordered "I Love Science", and 20 students who ordered "The King of Stories", and 7 of them ordered these two books. How many people in class one of the third grade ordered these two kinds of books?
三年级一班订《我爱科学》的同学有16人，订《故事大王》的同学有20人，其中有7人订了这两种书．三年级一班订这两种书的一共有多少人？
<gadget id="calculator">20 - 7</gadget>
<output>13</output>

<gadget id="calculator">16 + 13</gadget>
<output>29</output>

<result>29</result>