Complement and supplement of an angle

Can -7PI/6 (-210 degrees) have a complement and supplement.

Complement no because it has to be a positive degree.

Supplement if I add 30 degrees to -210 it becomes 180 is this possible?

It says that it has to be two positive angles whose sum is 180 degrees. So I think it can since the positive angle of -210 is 150 degrees.

Find a co-terminal angle in the same format

my angle is 3.8 radians

How can I find a co-terminal angle? would I add/subtract 6.283185307? I know I add 2pi if it was pi/4 or 360 degrees if it said 30 degrees.

Thanks