I know this is technically not a trig question, but it involves trig and I'm sure there are a lot of engineering majors/graduates here, so here goes. I'm in a statics class (this is a question from my physics class) but we haven't actually talked about this specific type of problem yet.

The problem says:

"A sailor in a small sailboat encounters shifting winds. She sails 2.00km east, then 3.50km southeast, and then an additional distance in an unknown direction. Her final position is 5.80km directly east of her starting point. Find the magnitude and direction of the third leg of her journey."

So it looks like I've given 3 of the 4 parts of a vector addition equation that involves three vectors and a resultant. The resultant and two vectors are given, and you have to find the third. I know how to add vectors (graphically, with trig, and using x and y components) but I'm not sure about how to do this one.

EDIT: Should I break each known vector down into it's components and substitute a variable in for the unknown components of the third vector and from there solve for the unknown vectors components? Basically working backward to find the vector?