The average of three numbers is 4.2, the first number is 4.25, the first number is 0.3 more than the second number, what is the third number.
三个数的平均数为4.2，其中第一个数是4.25，第一个数比第二个数多0.3，第三个数是多少．
<gadget id="calculator">4.2 * 3</gadget>
<output>12.6</output>

<gadget id="calculator">4.25 - 0.3</gadget>
<output>3.95</output>

<gadget id="calculator">12.6 - 4.25 - 3.95</gadget>
<output>4.4</output>

<result>4.4</result>