The average of the five numbers is 20.68, the average of the first three numbers is 18.9, and the average of the last three numbers is 28.4. What is the middle number?
五个数的平均数是20.68，前三个数的平均数是18.9，后三个数的平均数是28.4，中间的数是多少？
<gadget id="calculator">18.9 * 3</gadget>
<output>56.7</output>

<gadget id="calculator">28.4 * 3</gadget>
<output>85.2</output>

<gadget id="calculator">56.7 + 85.2</gadget>
<output>141.9</output>

<gadget id="calculator">20.68 * 5</gadget>
<output>103.4</output>

<gadget id="calculator">141.9 - 103.4</gadget>
<output>38.5</output>

<result>38.5</result>