Let \( P \) be the point \( (10, -2, -1) \) and \( Q \) be the foot of the perpendicular drawn from the point \( R(1, 7, 6) \) on the line passing through the points \( (2, -5, 11) \) and \( (-6, 7, -5) \). Then the length of the line segment \( PQ \) is equal to:
