Originally, the ratio of male to female students in primary school was 7:5. Later, 12 girls were transferred. At this time, the ratio of male to female students was 9:7. How many boys are there in the school?
小学原来男女生的比是7：5，后来转来12名女生，这时男女生的比是9：7，学校现有男生多少人？
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(7/9) - (5/7)</gadget>
<output>4/63 = around 0.063492</output>

<gadget id="calculator">12 / (4/63)</gadget>
<output>189</output>

<result>189</result>