Compare drift velocity

Using the given formula , take the ratio of drift velocities  for two wires

v = e V T / ml  ; v = drift velocity , V = pot. difference , t = av. relaxation time , m = electronic mass , l = length

then substitute V = ml i / nae²T 

In case of series , current will be same , hance factor, 'i' will get cancelled.

in case of parallel , replace 'i' accordingly , using ohm's law.