I wish you would of put a picture but with what you gave me. if the angle is a straight line then you would just set it up like 96+x=180 bc a straight line ='s 180 and den subtract 96 from 180 which is 84 so x would = 84 if the angle is a supp. angle but til there's not a picture this might be wrong.
But i hope this helps have a nice nite!