The average of three numbers is 12.5. It is known that the first number is 10.5, the second number is 11.5, and the third number is known.
三个数的平均数是12.5，已知第一个数是10.5，第二个数是11.5，第三个数是多少．
<gadget id="calculator">12.5 * 3</gadget>
<output>37.5</output>

<gadget id="calculator">37.5 - 10.5 - 11.5</gadget>
<output>15.5</output>

<result>15.5</result>