Which of the following is equal to $20(x+y)-19(y+x)$ for all values of $x$ and $y$ ?
(A) $39 x+39 y$
(B) $x+y$
(C) $39 x+y$
(D) $x+39 y$
(E) $19 x-18 y$
Simplifying, we see that $20(x+y)-19(y+x)=20 x+20 y-19 y-19 x=x+y$ for all values of $x$ and $y$.

ANSWER: (B)