The agricultural machinery station has 840 kilograms of diesel oil. After 8 days of use, there are still 640 kilograms left. How many kilograms are used on average per day?
农机站有840千克柴油，用了8天，还剩下640千克，平均每天用多少千克？
<gadget id="calculator">840 - 640</gadget>
<output>200</output>

<gadget id="calculator">200 / 8</gadget>
<output>25</output>

<result>25</result>