A barrel of oil, half of which is poured out each time, after being poured three times, the weight of the barrel is 8 kg, and the known weight of the barrel is 3 kg. How many kilograms of oil is in the barrel?
一桶油，每次倒出一半，倒了三次后连桶重8千克，已知桶重3千克．原来桶里有油多少千克．
<gadget id="calculator">8 - 3</gadget>
<output>5</output>

<gadget id="calculator">5 * 2 * 2 * 2</gadget>
<output>40</output>

<result>40</result>