Use a glass to pour water into an empty bottle. If 3 cups of water are poured in, the total weight of the bottle is 240 kg. If 5 cups of water are poured in, the total weight of the bottle is 400 kg. How much does the glass of water weigh in kilograms?
用一个杯子向一个空瓶里倒水．如果倒进3杯水，连瓶共重240千克．如果倒进5杯水，连瓶共重400千克．问这一杯水重多少千克．
<gadget id="calculator">400 - 240</gadget>
<output>160</output>

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

<gadget id="calculator">160 / 2</gadget>
<output>80</output>

<result>80</result>