Pour water from a thermos vector cup, filling the measuring cup each time. If it is poured 4 times, it will be 200 ml more; if it is poured 6 times, it will be 600 ml less. What is the capacity of this hot water bottle in milliliters?
从一个热水瓶向量杯里倒水，每次都将量杯倒满．若倒4次，则多200毫升；若倒6次，则少600毫升．这个热水瓶的容量是多少毫升？
<gadget id="calculator">600 + 200</gadget>
<output>800</output>

<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">800 / 2</gadget>
<output>400</output>

<result>400</result>