Use a cup to pour water into an empty bottle. After pouring 4 cups of water, the weight of the bottle is 280 grams. After pouring 7 cups of water, the weight of the bottle is 400 grams. How many grams does a glass of water weigh?
用一个杯子向空瓶里倒水，倒入4杯水后连瓶重280克，倒入7杯水后连瓶重400克，一杯水重多少克？
<gadget id="calculator">400 - 280</gadget>
<output>120</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<result>40</result>