A certain class of girls accounted for the whole class (4/7), and later 2 girls were transferred, and girls only accounted for the whole class (5/9), how many girls are there in this class? (Solve with formula).
某班女生占全班人数(4/7)，后来转走2名女生，女生只占全班人数(5/9)，这个班现有女生多少人？(用算式解答)．
<gadget id="calculator">7 - 4</gadget>
<output>3</output>

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

<gadget id="calculator">9 - 5</gadget>
<output>4</output>

<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(4/3) - (5/4)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">2 / (1/12)</gadget>
<output>24</output>

<gadget id="calculator">24 * (5/4)</gadget>
<output>30</output>

<result>30</result>