There are 81 kilograms of rice in the cafeteria. After eating for 7 days, there are still 18 kilograms left. How many kilograms are eaten per day on average?
食堂有81千克大米，吃了7天，还剩18千克，平均每天吃了多少千克？
<gadget id="calculator">81 - 18</gadget>
<output>63</output>

<gadget id="calculator">63 / 7</gadget>
<output>9</output>

<result>9</result>