The ratio of the number of girls to the number of boys in the sixth grade is 3:4, and the number of boys transferred in the new semester is 15. This means that the ratio of the number of girls to boys is 2:3. How many girls are there in the sixth grade?
六年级女生人数与男生人数的比是3：4，新学期转入男生人数15人，这是女生与男生人数的比是2：3，六年级有女生多少人？
<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(3/2) - (4/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">15 / (1/6)</gadget>
<output>90</output>

<result>90</result>