Sorry you've not had any responses about this. Are you sure you’ve posted in the right place? Posting in the specific Study Help forum should help get responses.
I'm going to quote in Tank Girl now so she can move your thread to the right place if it's needed.
The way i would answer these types of questions is by deriving formulas
I = dq/dt ....(1) [by definition] d = vdt ....(2) [by definition]
dq/dt=I = nAd [ charge concentration / cross section] I = nAvdtdq/dt
v = I/nAdq from this expression you may conclude that the drift velocity is indipendent of length of whatever the charges are passing through at this level. Try to translate these equations into words yourself. hope this helps!