The following system of equations does not have a unique solution.
⎩⎨⎧6x+ky+2z=a6x−y−z=72x−3y+z=1
(1) (a) Find the value of k.
(2) Each equation represents a plane.
(b) Find
(i) the value of a for which the three planes intersect in a line
(ii) the equation of the line.
(3) (c) If the value of a is such that the three planes do not intersect in a line, describe their geometric configuration, justifying your answer.