How do I choose the correct angle when graphing vectors from unit notation?

[tunze]

Homework Statement

Draw the following vector. Label the angle that specifies the vector's direction, then find its magnitude and direction.

Homework Equations

vector a = 2.0i - 6.0j

The Attempt at a Solution

I get stuck here:

I don't know which angle to use.

 

[tunze]

I used the red one but the back of the book uses the brown one :/