The ratio of boys to girls in a certain class is 6:7, there are 39 students in the class, how many girls are there? (solution with equation)
某班男生人数与女生人数的比是6：7，全班有39人，求女生有多少人？(用方程解答)
<gadget id="calculator">6 + 7</gadget>
<output>13</output>

<gadget id="calculator">39 / 13</gadget>
<output>3</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<result>21</result>