There are 20 small balls in red, green, and yellow. It is known that the number of red balls is 6 times that of yellow balls. How many green balls are there at least? (Click for ideas: there are at most 2 yellow balls)
有红、绿、黄三种颜色的小皮球共20个，已知红皮球的个数是黄皮球的6倍，那么绿皮球至少有多少个？(思路点击：黄皮球最多有2个)
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">20 - 12 - 2</gadget>
<output>6</output>

<result>6</result>