I think that the easiest way to do things like this is to convert everything from radians to degrees. to do this, you can make a proportion. (pi/8)/pi = x/180. (We know that pi radians is 180 degrees.) Then you can solve for x. The pis cancel out and you are left with 1/8 = x/180. Multiply both sides by 180 and you get 22.5 =x. Then the complement is 90-22.5=67.5 and the supplement is 180-22.5=157.5. To convert these back to radians you can make another proportion.
67.5/180=x/pi
.375=x/pi
.375pi = x is the complement
157.5/180=x/pi
.875=x/pi
.875pi = x is the supplement.
Hope this helped!