There are 15 people in the mathematics interest group, and 12 people in the art group. The number of people in the two groups is exactly the number of people in the sports group (9/13). How many people are there in the sports group?
数学兴趣小组有15人，美术小组有12人，两个小组的人数刚好是体育小组人数的(9/13)，体育小组有多少人？
<gadget id="calculator">15 + 12</gadget>
<output>27</output>

<gadget id="calculator">9 / 13</gadget>
<output>9/13 = around 0.692308</output>

<gadget id="calculator">27 / (9/13)</gadget>
<output>39</output>

<result>39</result>