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

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