A set of data is arranged from small to large, a total of 6, 3, 4, □, □, 10, 21, their median is 8, what is the average of these 6 numbers
一组数据从小到大排列共6个，3，4，□，□，10，21，它们的中位数是8，这6个数的平均数是多少
<gadget id="calculator">3 + 4 + 16 + 10 + 21</gadget>
<output>54</output>

<gadget id="calculator">54 / 6</gadget>
<output>9</output>

<result>9</result>