The average of three numbers is 18, two of which are 26 and 16, what is the third number.
三个数的平均数是18，其中两个数是26和16，第三个数是多少．
<gadget id="calculator">18 * 3</gadget>
<output>54</output>

<gadget id="calculator">54 - 26 - 16</gadget>
<output>12</output>

<result>12</result>