Take the desired point to be X= (x, y, z). The vector from point A to X is xi+ (y+2)j+ (z- 1)k.

The unit vector in that direction is

The vector from point B to x is (x- 4)k+ (y-3)j+ (z+ 5)k.

The unit vector in that direction is

The normal to the plane is given by the vector i+ 3j+ 2k.

The unit normal is

The physical law here is that the light rays must make the same angle with the perpendicular. That that means that the dot products of each of those first two unit vectors with the unit normal must be the same.