$$\textbf{Step 1: Creating an equation.}$$
$$\text{Distance between the plane and sea level = 5000m}$$
$$\text{Distance between the submarine and sea level = 1200m}$$
$$\text{Vertical distance = Distance between the submarine and sea level }$$
$$\text{+ Distance between the plane and sea level}$$
$$\textbf{Step 2: Substituting the values and solving the equation.}$$
$$\text{Vertical distance = Distance between the submarine and sea level }$$
$$\text{+ Distance between the plane and sea level}$$
$$\text{Vertical distance} = 1200 + 5000$$
$$\text{Vertical distance = 6200m}$$
$$\textbf{Hence, the vertical distance between the plane and submarine is equal to 6200m}$$