The average of three numbers is 12, and the average after adding one number is 11.5, what is the added number?
三个数的平均数是12，加上一个数后平均数是11.5，加上的数是多少．
<gadget id="calculator">11.5 * 4</gadget>
<output>46</output>

<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">46 - 36</gadget>
<output>10</output>

<result>10</result>