Straight Lines And Pair Of Straight Lines

When the origin is shifted to the point $(2, b)$ by translation of axes, the coordinates of the point $(a, 4)$ have changed to $(6,8)$. When the origin is shifted to $(a, b)$ by translation of axes, if the transformed equation of $x^2+4 x y+y^2=0$ is $X^2+2 H X Y+Y^2+2 G X+2 F Y+C=0$, then $2 H(G+F)=$