1. **State the problem:** We need to find the distance between a bird flying 3500 m above sea level and a diver 40 m below sea level. 2. **Understand the positions:** The bird is at +3500 m and the diver is at -40 m relative to sea level (0 m). 3. **Formula:** The distance between two points on a vertical scale is the absolute difference of their heights: $$\text{Distance} = |h_1 - h_2|$$ where $h_1$ and $h_2$ are the heights of the bird and diver respectively. 4. **Calculate the distance:** $$\text{Distance} = |3500 - (-40)| = |3500 + 40| = |3540| = 3540$$ 5. **Interpretation:** The bird is 3540 meters away from the diver vertically. **Final answer:** The bird is 3540 meters from the diver.