Use a cup to pour water into an empty jug. If 2 cups of water are poured into it, the weight of the jug is 640 grams; if 5 cups of water are poured into it, the weight of the jug is 880 grams. How many grams does each cup of water weigh?
用一个杯子向空水壶里倒水，如果倒进2杯水，连壶重640克；如果倒进5杯水，连壶重880克．每杯水重多少克？
<gadget id="calculator">880 - 640</gadget>
<output>240</output>

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

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

<result>80</result>