The average of nine numbers is 16. If one of the numbers is changed to 30, then the average of these nine numbers is 18. What is the changed number?
九个数，平均数是16，如果把其中一个数改为30，那么这九个数的平均数是18，则改动的这个数原来是多少．
<gadget id="calculator">18 * 9</gadget>
<output>162</output>

<gadget id="calculator">16 * 9</gadget>
<output>144</output>

<gadget id="calculator">162 - 144</gadget>
<output>18</output>

<gadget id="calculator">30 - 18</gadget>
<output>12</output>

<result>12</result>