If $x=4$ and $x+y=0$, what is the value of $y$ ?
(A) 0
(B) -2
(C) -3
(D) -1
(E) -4
Since $x+y=0$, then $x$ and $y$ must be opposites.

Since $x=4$, then $y=-4$, and we may check that $4+(-4)=0$.

ANswer: (E)