What is the average of the four numbers 90, 89, 88, and 89?
90、89、88、89这四个数的平均数是多少．
<gadget id="calculator">90 + 89 + 88 + 89</gadget>
<output>356</output>

<gadget id="calculator">356 / 4</gadget>
<output>89</output>

<result>89</result>