We need to find relative speed between two ships.
We look at relative speed along the north direction and west direction.
[tex]N: v_b_n-v_a_n=v_b_n\\ W:v_a_w-v_b_w=v_a_w\\[/tex]
This is because boats are travaling at directions that are perpedincular to each other. Total relative speed is:
[tex]v_r=\sqrt{v_a_w^2+v_b_n^2}=\sqrt{22^2+23^2}=31.83[/tex]
And that is how fast they are moving away from eachother.
Please note that these boats are not accelerating, therefore the distance between them is increasing at the constant rate.
