Given that the altitudes of A and B are -70m and 20m respectively, how much is the difference in altitude between A and B?
已知A，B两地的海拔高度分别为-70m，20m，则A，B两地海拔相差多少m
<gadget id="calculator">20 - (-70)</gadget>
<output>90</output>

<result>90</result>