(Contest question) A barrel of oil weighs 138.4 kilograms. After half of it is used up, the remaining oil weighs 75.5 kilograms. How much does the barrel weigh?
(竞赛题)一桶油，连桶共重138.4千克，用去一半后，剩下的油连桶重75.5千克，油桶重多少千克？
<gadget id="calculator">138.4 - 75.5</gadget>
<output>62.9</output>

<gadget id="calculator">62.9 * 2</gadget>
<output>125.8</output>

<gadget id="calculator">138.4 - 125.8</gadget>
<output>12.6</output>

<result>12.6</result>