A barrel of oil weighs 32.1 kilograms. After half of the oil is poured out, the weight of the barrel is still 17.1 kilograms. How many kilograms does this barrel of oil weigh?
一桶油连桶重32.1千克，倒出一半油后连桶重还有17.1千克，原来这桶油有多少千克？
<gadget id="calculator">32.1 - 17.1</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>