# What is the complement and supplement of 18.y degree?

Do you mean ${18}^{o}$?
If so, the complement is 72^o" and the supplement is 162^o#.
The complement of an angle is a second angle that adds to the first to make a right angle. So subtract any angle measure that's less than ${90}^{o}$ from ${90}^{o}$.
Likewise, the supplement of an angle is the angle you add to the original to make ${180}^{o}$.