The cafeteria bought 9 barrels of oil, 4 kilograms per barrel, and used 8 kilograms. How many kilograms are left?
食堂买来9桶油，每桶4千克，用了8千克，还剩多少千克？
<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<gadget id="calculator">36 - 8</gadget>
<output>28</output>

<result>28</result>