Thank you! (I would rep but SR won't let me) :P
Last question,
where did I go wrong in part d?As P and M are perpendicular to each other I made P into a plane that is parallel to M and then put it in the form r.n(unit vector) = d(unit vector)
for M: r . 1/root14(2, 1, 3) = 21/root14
for P: r . 1/root14(2, 1, 3) = (1, 2, 1) . (2, 1, 3)
= 7/root14
so it's 21-7/root14 = root14