Two barrels of oil weigh 20 kilograms in total. If 4 kilograms are poured out of barrel A, the two barrels have the same amount of oil. How many kilograms of oil does barrel A contain?
两桶油共重20千克，如果从甲桶倒出4千克，两桶油就一样多，原来甲桶有油多少千克．
<gadget id="calculator">20 + 4</gadget>
<output>24</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<result>12</result>