5. Find the number of integer pairs $x, y$ such that $x y-3 x+5 y=0$.
(A) 1
(B) 2
(C) 4
(D) 8
(E) 16
5. Answer: (D)
$x y-3 x+5 y=0$ is equivalent to $(x+5)(y-3)=-15$.
If $x+5=a$ and $y-3=b$, then there are eight distinct pairs of integers $a, b$ (counting signs) such that $a b=-15$.