The altitude of A is -30 meters, and the altitude of B is 10 meters. What is the difference in meters between A and B?
A地海拔高度是-30米，B地海拔高度是10米，A、B两地地势相差多少米．
<gadget id="calculator">10 - (-30)</gadget>
<output>40</output>

<result>40</result>