There are a number of students reading in the school library, and girls account for (4/9). Later, 104 girls came in. At this time, the ratio of girls to the number of people reading is 21:31. How many students were reading?
学校图书馆里有若干名学生在看书，女生占(4/9)，后来有104名女生进来，这时女生和看书人数的比是21：31，原来有多少名学生在看书？
<gadget id="calculator">31 - 21</gadget>
<output>10</output>

<gadget id="calculator">21 / 10</gadget>
<output>21/10 = around 2.1</output>

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

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(21/10) - (4/5)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 - (4/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">104 / (13/10) / (5/9)</gadget>
<output>144</output>

<result>144</result>