Angular momentum about an origin (O,O,O)

[Tui]

Homework Statement

Calculate the angular momentum about the origin O=(0,0,0) of a particle of mass m moving
along the following two trajectories:

(a) x(t)=vt y(t)=b z(t)=0
(b) x(t)=Rcos(wt) y(t)= Rsin(wt) z(t)=vt

Homework Equations

L = r x p
L = mvr

The Attempt at a Solution

I wasn't really sure to begin. I thought maybe I could do
L= m(vxr)
L=m ( (mv,0,0)x(vt...) Not sure what the vector equation for P is and also not sure what to do about the mass

Please help!

 

[Tui]

Any help is GREATLY appreciated D: Kinda urgent