find a unit vector in the plane containing P x q

Sep 2011
49
0
given p=(1,4,1), q=(2,1,-1) and r=(1,-3,2) find:

a) a unit vector perpendicular to the plane containing p and q

b) a unit vector in the plane containing P x q and p x r that has zero x component.

I know how to calculate a) is (-5, 3, -7)/root of 83
but how to do it b)?