Straight Lines And Pair Of Straight Lines

Let $L_1, L_2$ be the lines represented by the equation $4 x^2-5 x y+3 y^2=0$. Let $L_3, L_4$ be two lines passing through the point $(4,3)$ such that $L_3$ and $L_4$ are perpendicular to $L_1$ and $L_2$ respectively. If the combined equation of $L_3$ and $L_4$ is $a x^2+2 h x y+b y^2+2 g x+2 f y+c=0$, and $a f+b g+c h=$