The average of three numbers is 4.2, the first number is 4.25, the second number is 0.3 more than the first number, what is the third number.
三个数的平均数是4.2，其中第一个数是4.25，第二个数比第一个数多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>4.55</output>

<gadget id="calculator">12.6 - 4.25 - 4.55</gadget>
<output>3.8</output>

<result>3.8</result>