Let \(n\) be a positive integer. If the equation \(2x+2y+z=n\) has \(28 \) solutions in positive integers \(x, y, \) and \(z\), then \(n\) must be either
(A) 14 or 15
(B) 15 or 16
(C) 16 or 17
(D) 17 or 18
(E) 18 or 19
The answer is (E) 18 or 19.
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