Straight Lines And Pair Of Straight Lines

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 equation of the incident ray is \(a x+b y+1=0\), then \(a^2+b^2+3 a b\) is equal to _________.