The average of five numbers is 19.68, the average of the first three numbers is 18.9, and the average of the last three numbers is 29.4. What is the middle number?
有五个数的平均数是19.68，前三个数的平均数是18.9，后三个数的平均数是29.4，中间一个数是多少？
<gadget id="calculator">145 - 98.4</gadget>
<output>46.6</output>

<result>46.6</result>