Li Ming's books are three times that of Zhang Hong's. If Zhang Hong gives Li Ming 7 books, Li Ming will have 5 times as many books as Zhang Hong. How many copies does Zhang Hong have?
李明的图书是张宏的3倍．如果张宏给李明7本，则李明的图书本数是张宏的5倍．张宏有多少本？
<gadget id="calculator">7 * 5</gadget>
<output>35</output>

<gadget id="calculator">35 + 7</gadget>
<output>42</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>