In the mathematics interest group last semester, boys accounted for (5/9). After adding 21 girls this semester, boys accounted for only (2/5). How many people are there in this group now?
数学兴趣小组上学期男生占(5/9)，这学期增加21名女生后，男生只占(2/5)，这个小组现在有多少人．
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

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

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

<gadget id="calculator">(3/2) - (4/5)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">21 / (7/10) / (2/5)</gadget>
<output>75</output>

<result>75</result>