The sixth grade subscribes to "Selected Compositions of Primary School Students" and "Primary School Students' Study Newspaper". , there are 6 people who ordered both of these, how many people ordered "Selected Compositions for Primary School Students"?
六年级征订《小学生作文选》和《小学生学习报》，每人至少订一种，全年级学生的(3/5)订了《小学生作文选》，(4/7)订了《学习报》，这两种都订的有6人，订《小学生作文选》的有多少人？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) - 1</gadget>
<output>-3/7 = around -0.428571</output>

<gadget id="calculator">(3/5) + (-3/7)</gadget>
<output>6/35 = around 0.171429</output>

<gadget id="calculator">6 / (6/35)</gadget>
<output>35</output>

<gadget id="calculator">35 * (3/5)</gadget>
<output>21</output>

<result>21</result>