The average of three numbers is 8.4, the first number is 9.6, the second number is 8, what is the third number?
三个数的平均数是8.4，其中第一个数是9.6，第二个数是8，第三个数是多少？
<gadget id="calculator">8.4 * 3</gadget>
<output>25.2</output>

<gadget id="calculator">9.6 + 8</gadget>
<output>17.6</output>

<gadget id="calculator">25.2 - 17.6</gadget>
<output>7.6</output>

<result>7.6</result>