A bottle of oil weighs 900 grams. After half of the oil is poured out, the weight of the bottle is 600 grams. What is the weight of the bottle?
一瓶油连瓶重900克，倒去一半油后连瓶重600克，瓶子重多少克．
<gadget id="calculator">900 - 600</gadget>
<output>300</output>

<gadget id="calculator">300 * 2</gadget>
<output>600</output>

<result>300</result>