There are 27 red balloons, 3 fewer yellow balloons than red balloons, twice as many yellow balloons as green balloons, how many green balloons are there?
红气球有27只，黄气球比红气球少3只，黄气球是绿气球的2倍，绿气球有多少只？
<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<result>12</result>