3d Geometry

Let the point A be the foot of perpendicular drawn from the point P$(a, b, 0)$ on the line

\(\frac{x-1}{2} = \frac{y-2}{1} = \frac{z-\alpha}{3}.\)

If the midpoint of the line segment PA is \(\left(0, \frac{3}{4}, -\frac{1}{4}\right),\) then the value of $a^2 + b^2 + \alpha^2$ is equal to :