Use a cup to pour water into an empty bottle. If 6 cups of water are poured into it, the total weight of the bottle is 680 grams. If 9 cups of water are poured into it, the total weight of the bottle is 920 grams. What is the weight of the empty bottle in grams?
用杯子往一个空瓶里倒水，如果倒进6杯水，连瓶共重680克，如果倒进9杯水，连瓶共重920克，空瓶的重量是多少克．
<gadget id="calculator">920 - 680</gadget>
<output>240</output>

<gadget id="calculator">240 / 3</gadget>
<output>80</output>

<gadget id="calculator">6 * 80</gadget>
<output>480</output>

<gadget id="calculator">680 - 480</gadget>
<output>200</output>

<result>200</result>