Uncle Wang sprayed a total of 840 trees from 8:00 am to 3:00 pm. How many trees does he spray on average per hour?
王叔叔从早晨8时到下午3时，共给840棵树喷了药水，他平均每小时喷多少棵树？
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">840 / 7</gadget>
<output>120</output>

<result>120</result>