Find the reference angle when o= 420 degrees a) 30 degrees b) 45 degrees c) 50 degrees d) 120 degrees

Consider the unit circle, with the number of degrees, from 0 to 360, describing the counterclockwise rotation. 360 degrees is one complete revolution (back to the original point, 0°). Therefore, let's subtract 360 from 420 to see where we would end up on the unit circle:
420 - 360 = 60° 
In the first quadrant (0 - 90° on the unit circle), the reference angle is equal to the angle itself. In this case, the reference angle is 60°. Answer is not included, which indicates there may be an transcription error in the problem.