Use a cup to pour water into a bottle. If 3 cups of water are poured into it, the total weight of the bottle is 540 grams; if 5 cups of water are poured into it, the total weight of the bottle is 680 grams. How many grams does an empty bottle weigh?
用一个杯子向一只瓶子里倒水，如果倒进3杯水，连瓶共重540克；如果倒进5杯水，连瓶共重680克，一只空瓶重多少克？
<gadget id="calculator">680 - 540</gadget>
<output>140</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">140 / 2</gadget>
<output>70</output>

<gadget id="calculator">70 * 3</gadget>
<output>210</output>

<gadget id="calculator">540 - 210</gadget>
<output>330</output>

<result>330</result>