Let a ray of light passing through the point (3,10) reflects on the line 2 x+y=6 and the reflected ray passes through the point (7, 2). If the…

Let a ray of light passing through the point $\displaystyle (3,10)$ reflects on the line $\displaystyle 2 x+y=6$ and the reflected ray passes through the point $\displaystyle (7, 2)$. If the equation of the incident ray is $\displaystyle a x+b y+1=0$, then $\displaystyle a^2+b^2+3 a b$ is equal to $\displaystyle \_\_\_\_$.