Use a cup to pour water into a bottle. If 5 cups of water are poured into the bottle, the total weight of the bottle is 300 grams; if 7 cups of water are poured, the total weight of the bottle is 440 grams. How much does a glass of water weigh in grams?
用一个杯子往瓶子里倒水，如果倒进5杯水，连瓶子共重300克；如果倒进7杯水，连瓶子共重440克．一杯水重多少克．
<gadget id="calculator">440 - 300</gadget>
<output>140</output>

<gadget id="calculator">7 - 5</gadget>
<output>2</output>

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

<result>70</result>