If the mean, mode, and median of the five numbers 9, 5, 4, 18, and □ are all equal, then what is the possible number in □.
如果9、5、4、18、□这五个数的平均数、众数、中位数都相等，那么□里可能是多少．
<gadget id="calculator">9 + 5 + 4 + 18 + 9</gadget>
<output>45</output>

<gadget id="calculator">45 / 5</gadget>
<output>9</output>

<result>9</result>