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 440 grams. If 4 cups of water are poured into it, the total weight of the bottle is 520 grams. What is the weight of a glass of water in grams?
用一个杯子向一只瓶子里倒水，如果倒进3杯水，连瓶共重440克，如果倒进4杯水，连瓶共重520克，则一杯水重多少克．
<gadget id="calculator">520 - 440</gadget>
<output>80</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">80 / 1</gadget>
<output>80</output>

<result>80</result>