In the last semester, the ratio of the number of girls to the whole class was 3:7. After 2 girls were transferred out this semester, the ratio of the number of girls to the whole class was 2:5. How many students are there in class 6 and 4 this semester?
上学期六4班女生人数与全班人数的比是3：7，本学期转出2位女生后，女生人数与全班人数的比是2：5．本学期六4班有学生多少人？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 2</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 - (4/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(3/7) - (2/5)</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">(6/5) / (1/35)</gadget>
<output>42</output>

<result>42</result>