The altitude of point A is 30 meters, the altitude of point B is 25 meters, and the altitude of point C is -15 meters. Which point is the highest? Which point is the lowest? How many meters higher is the highest point than the lowest point?
A点海拔高度为30米，B点的海拔高度为25米，C点的海拔高度为-15米，哪个点最高？哪个点最低？最高点比最低点高多少米？
<gadget id="calculator">30 - (-15)</gadget>
<output>45</output>

<result>45</result>