Use a glass to pour water into an empty bottle, and the glass is always full. If 2 cups of water are poured, the weight of the bottle is 1300g; if 5 cups of water are poured, the weight of the bottle is 3100g, what is the weight of the bottle?
用一个杯子向一个空瓶里面倒水，每次都是满杯．如果倒进2杯水，则连瓶重1300g；如果倒进5杯水，则连瓶重3100g，瓶重多少g．
<gadget id="calculator">3_100 - 1_300</gadget>
<output>1_800</output>

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

<gadget id="calculator">1_800 / 3</gadget>
<output>600</output>

<gadget id="calculator">600 * 2</gadget>
<output>1_200</output>

<gadget id="calculator">1_300 - 1_200</gadget>
<output>100</output>

<result>100</result>