Altitude of mountain climber is 4572 and altitude of submarine commander is - 609. What is the the difference in their altitude

To have a minus altitude or negative altitude you need to go below 0 (which is represented by the sea level).

To get the difference between the mountain climber and submarine commander you add both altitudes as positive numbers: 4572 + 609 = 5181 m difference!

Another ex.

If a scuba diver is under the water, say 10 m hhe has a altitude of - 10m

And a submarine is under at 100m that is a altitude of - 100m.

The difference between the two is 100-10=90 m, not - 90m. The difference is always a positive number.