A "McDonald's" shop needs to serve 300 kilograms of French fries. It has been served 3 times, with an average of 40 kilograms of French fries each time. How many kilograms of French fries are left unfinished.
一家"麦当劳"店要配300千克的薯条，已经配了3次，平均每次配40千克的薯条，还剩多少千克薯条没有配完．
<gadget id="calculator">400 - 120</gadget>
<output>280</output>

<result>280</result>