barrel of oil weighs 62.8 kilograms. After half of the oil is used, the weight of the barrel is 33.5 kilograms. How much does the barrel weigh?
一桶油连桶重62.8千克，用去一半油后，连桶重33.5千克，油桶重多少千克？
<gadget id="calculator">62.8 - 33.5</gadget>
<output>29.3</output>

<gadget id="calculator">29.3 * 2</gadget>
<output>58.6</output>

<gadget id="calculator">62.8 - 58.6</gadget>
<output>4.2</output>

<result>4.2</result>