2.) The 15 degrees is the direction of the vectors and the 12 m/s and 5 m/s are the magnitudes of the vectors. If you draw out the vectors, you will see that they intersect at a right angle. Thus, using the "tip-to-tail" method of adding vectors is just the Pythagorean Theorem: . So it is going 13 m/s. To find its angle with the origin, you need to start by taking . However, this gives you the one of the angles of the 5-12-13 triangle, not the angle the 13 m/s vector makes with the origin. To find this angle, subtract from the angle you found above to get . So the boat travels at 13 m/s in the direction east of north.
I'm sure that was confusing but if you draw out the picture it should be easier to understand.