A barrel of oil weighs 45 kilograms in total. After half of it is used up, the total weight of the barrel is 23.5 kilograms. How many kilograms does the oil weigh?
一桶油连桶共重45千克，用去一半后连桶共重23.5千克，油重多少千克？
<gadget id="calculator">45 - 23.5</gadget>
<output>21.5</output>

<gadget id="calculator">21.5 * 2</gadget>
<output>43</output>

<result>43</result>