Relative velocity of 2 vehicles

[Aashish Bharat]

Two vehicles leave simultaneously from a fork in a road. Vehicle A travels at a velocity of 85 km/h north-east. Vehicle B travels at 104 km/h directly east. Calculate the velocity of vehicle A relative to the velocity of vehicle B.

Answer (from memorandum): http://imgur.com/a/L0prH

I do not understand why is Vehicle B traveling west, an explanation on how why this was done would be appreciated!

aVb = Va - Vb (Velocity of A relative to velocity of B) when do you use this equation?

 

[PeroK]

If you are in a car and get overtaken by another car, then relative to the faster car you are going backwards. Not so?

 

[Aashish Bharat]

If you are in a car and get overtaken by another car, then relative to the faster car you are going backwards. Not so?

Damn it, they took the opposite direction of Vb from the equation aVb = Va - Vb. I should have known better