Three Dimensional Geometry: JEE Main 2022 Mathematics question

Let the mirror image of the point (a, b, c) with respect to the plane 3x $-$ 4y + 12z + 19 = 0 be (a $-$ 6, $\beta$, $\gamma$). If a + b + c = 5, then 7$\beta$ $-$ 9$\gamma$ is equal to ______________.