vector急

let va=i+2j-3k, vb=i+j+k, c= i-j+k and P be the plane containing va and vb.
given that:
va and vb are orthogonal
volume of the parallelepiped with va,vb and vc as its sides=8
a unit vector vn perpendicular to the plane P=(5i-4j-k)/+(42)^0.5 OR (5i-4j-k)/-(42)^0.5

a) find the angle between vc and P in radian. Give the ans corr. to 2 d.p
b) find the two vectors u and v such u+v=c, wherer u is perpendicular to P and v lies on P. ( u,v and c are vectors)

thanks