Girls in a certain class account for (3/7) of the whole class, and after 6 girls are transferred from other places, the number of girls accounts for (1/2) of the whole class. How many girls are there in this class?
某班女生占全班人数的(3/7)，从外地转来6名女生后，女生人数占全班人数的(1/2)．这个班原有女生多少名？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / (1/2)</gadget>
<output>1</output>

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

<gadget id="calculator">1 - (3/7)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(3/7) / (4/7)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">6 / (1/4)</gadget>
<output>24</output>

<gadget id="calculator">24 * (3/4)</gadget>
<output>18</output>

<result>18</result>