The mirror's equation is represented by the line: \[ \frac{x}{1} = \frac{1 - y}{2} = \frac{2z - 4}{6}. \] This can be expressed parametrically with parameter \( t \) as: \[ x = t, \quad y = 1 - 2t, \quad z = \frac{6t + 4}{2} = 3t + 2. \] The point \( P(1, 6, 3) \) is at a distance from this mirror. The reflection of a point across a plane involves calculating the perpendicular distance to the plane and then locating the symmetric point. By using the reflection formula and solving for the reflected point \( P' \), we can determine the distance between \( P \) and \( P' \).