Answer:

Since the aeroplane is above the sea level, and the submarine is below the sea level. So, it is highly probable that the sea level is the reference datum or line.

Hence, we can make an equation like this.

H = A + S

Where A represents the aeroplane, S represents the submarine, and H represents the total height or the distance between the two objects.

H = 1 965 + 2 108

H = 4 073 m

I hope you understand my explanation.