The average of three numbers is 8.4, the first number is 8.8, which is 1.2 less than the third number, what is the second number?
三个数的平均数是8.4，第一个数是8.8，比第三个数小1.2，则第二个数是多少．
<gadget id="calculator">8.4 * 3</gadget>
<output>25.2</output>

<gadget id="calculator">8.8 + 1.2</gadget>
<output>10</output>

<gadget id="calculator">25.2 - 8.8 - 10</gadget>
<output>6.4</output>

<result>6.4</result>