Let \(ABCDE\) be a convex pentagon with \(AB || CE, BC || AD, AC || DE, \angle ABC=120^\circ, AB=3, BC=5,\) and \(DE = 15.\) Given that the ratio between the area of triangle \(ABC\) and the area of triangle \(EBD\) is \(m/n,\) where \(m\) and \(n\) are relatively prime positive integers, find \(m+n.\)
(第二十二届AIME2 2004 第13题)