Mirror, MirrorGeometry Level 3
The point \(P(5, 3)\) was reflected over a line in the \(x,y\) plane. Its resulting position was \(P'\) at \((-3, 9)\). The line it was reflected over can be written in standard form as \(Ax + By = C\) where \(A, B\), and \(C\) are integers with no common factors, and \(A\) is a positive integer. \(Find A + B + C\).