The surface of a lake is 180 meters above sea level and the bottom of the lake is 220 meters below sea level. How deep is the lake actually at this point?
一个湖的水面高出海平面180米，湖的底面则比海平面低220米．湖水在这一点实际有多少米深．
<gadget id="calculator">180 + 220</gadget>
<output>400</output>

<result>400</result>