Conceptually, you are asking for the additive inverse of 8. By definition, in fact, the additive inverse of a number [tex]x[/tex] is a number [tex] y [/tex] such that [tex] x+y=0 [/tex]
You obtain the additive inverse of a number by switching its sign, so the additive inverse of 8 is -8. In fact, you have
[tex] 8+(-8) = 8-8=0 [/tex]
