Determine whether $A (2, 2, 3)$, $B(4, 0, 7)$, $C (6, 3, 1)$ and $D (2, −3, 11)$ are in the same plane. 
a) Compute a suitable volume to determine whether $A  (2, 2, 3)$, $B 
(4, 0, 7)$, $C  (6, 3, 1)$ and $D  (2, −3, 11)$ are in the same plane.
b) Find the distance between the line $L$ through $A$, $B$ and the
  line $M$ through $C$, $D$.


My answer:
V = |(a-d) · ((b-d)x(c-d))| / 6
= -15/2
  Thoughts? Help?!?!

Hint:) Idea is, the volume made by three vectors $u$, $v$ and $w$ is
$$u.(v\times w)$$
so with four points we can make three vectors and if this volume be zero, then these vectors and correspondence, four points lie on a plane.
