Working simultaneously at their respective constant rates, Machines \(A\) and \(B\) produce 800 nails in \(x\) hours. Working alone at its constant rate, Machine \(A\) produces 800 nails in \(y\) hours. In terms of \(x\) and \(y,\) how many hours does it take Machine \(B,\) working alone at its constant rate, to produce 800 nails?

(A) \(\dfrac{x}{x+y}\)
(B) \(\dfrac{y}{x+y}\)
(C) \(\dfrac{xy}{x+y}\)
(D) \(\dfrac{xy}{x-y}\)
(E) \(\dfrac{xy}{y-x}\)

[spoiler]OA=E[/spoiler]

Source: Official Guide