Important Vector question!!

Hi guys, I have this question which I really need help ...

The equation of a plane P1 in a cartesian coordinate system is given by 3x+y-z-6=0. THe cordinates of two points A and B are [1,1,3] and [2,1,2] respectively.

i)Find the unit vector normal to the plane P1.

ii)Find the vector** AB.**

iii)Find the equation of a plane P2 that passes thru the points A and B and is perpendicular to the plane P1.

so far i only got** AB=OB-OA** ..i think so which is equals to i-k.

A different, but longer way