The ratio of male to female employees in a certain unit is 3:4. After two female employees are transferred, the ratio of male to female employees is 5:7. How many female employees are there in this unit?
某单位男女职工的人数比是3：4，调来两名女职工后，男女职工的人数比是5：7，这个单位现有女职工多少人？
<gadget id="calculator">7 / 5</gadget>
<output>7/5 = around 1.4</output>

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

<gadget id="calculator">(7/5) - (4/3)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">2 / (1/15)</gadget>
<output>30</output>

<result>30</result>