A barrel of oil weighs 11 kilograms. After half of the oil is poured out, the weight of the barrel is 6.5 kilograms. How many kilograms does the barrel weigh?
一桶油连桶重11千克，倒出一半油后，连桶重6.5千克，桶重多少千克？
<gadget id="calculator">11 - 6.5</gadget>
<output>4.5</output>

<gadget id="calculator">4.5 * 2</gadget>
<output>9</output>

<gadget id="calculator">11 - 9</gadget>
<output>2</output>

<result>2</result>