Hi Guys. I don't know if this is the right section but I need some explanation on this (plz?)

a) Prove that a=b-kc and b=b+ka ( ) are collinear (a,b,c have those lines up that represent vectors)

b) Find so that vectors a=2i+3j and b= i-j can be collinear.

I know that these are probably simple but my brain isn't really working well.

Any help greatly appreciated.

Rinor