Points a is 5,623m above sea level. points b is below sea level at -1,245m. what is the distance between the two points?

If you go from point A to sea level, you need to go down 5,623 m.
If you go from point B to sea level, you need to go up 1,6,868 m245 m.
Add the two distances to find the distance between the points.

5,623 m + 1, 245 m = 6,868 m

Distances are always positive.  Find the distance of point A above sea level (sea level is our reference point).  Then find the distance of B below sea level (again remembering that distances are always positive).  Then sum up the resulting 2 positive numbers to obtain the distance between A and B:

5623 m + 1245 m = ?