(a) The given points are A (1, 1, −1), B (6, 4, −5), and C (−4, −2, 3).
Since A, B, C are collinear points, there will be infinite number of planes passing through the given points.
(b) The given points are A (1, 1, 0), B (1, 2, 1), and C (−2, 2, −1).

Therefore, a plane will pass through the points A, B, and C.

This is the Cartesian equation of the required plane.