Try drawing the rays. If you are looking at the ray through (-4,3) for example, you know that that -3/4 is the tangent of the angle the ray makes with either the positive x-axis or the negative x-axis. Use the diagram to figure out which it is, and then figure out the true angle.
For the second part, use the signs of the coordinates to determine which quadrant you are in. Then observe how the quadrant you are in determines the relationship between the reference angle and the true angle that you worked out in the first part.