For angles in first quadrant, the reference angle is itself. In second quadrant, the equation would be 180 - x where x is the measure of the angle. In third quadrant, x - 180. Lastly, in the fourth quadrant, the reference angle is 360 - x. From the second set of angles in the given, the reference angles are.
(1) 135 ; RA = 180 - 135 = 45
(2) 240; RA = 240 - 180 = 60
(3) 270; RA = 90 (lies in the y - axis)
(4) 330; RA = 360 - 330 = 30