A bucket of water weighs 20 kilograms, and after half of it is used up, the weight of the bucket is 11 kilograms. How much is the net weight of the bucket of water?
一桶水连桶重20千克，用去一半后，连桶重11千克，这桶水净重多少千克？
<gadget id="calculator">20 - 11</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>