Convert the angles to degrees. Remember there are 2pi radians in a circle, and a circle has 360 degrees, so conversion factor is 180degrees/pi. Then you can easily approximate the reference angle. Remember you make the reference angle from the positive x-axis and the reference angle will be the angle between the terminal side and the nearest x-axis (either positive side or negative side of the x-axis).
1)
2)
1)
2)