Vectors - Velocity of a moving object from another moving object

Hey!

I really didn't know what forum to put this under. I searched vectors, and threads came up in all sorts of different forums, including this one. I decided to put it here as this question is from a Calculus and Vectors course.

** Question: **

A liner is cruising at 18 knots in the direction S80W. A sailing vessel is moving at 6 knots in the direction N40W. Find the magnitude and direction of the velocity of the liner relative to the sailboat.

** Solution **

I am thinking that I should add these two vectors together to find the magnitude. I am unsure how to find the direction though. This problem is confusing me all over the place, can anyone help me by explaining how to solve this problem? A website with multiple examples similar to this one would be EXTREMELY helpful!

Thanks