  By using the quark-exchange formalism, realistic Faddeev wave functions and
Fermi motion effect, we investigate deep inelastic electron scattering from A=3
mirror nuclei in the deep-valence region. The initial valence quarks in put are
taken from the GRV's next-to-leading order calculations on $F_2^p(x,Q^2)$ which
give very good fit to the available data in the $(x,Q^2)$-plane. It is shown
that the free neutron to proton structure functions ratio can be extracted from
corresponding EMC ratios for $^3He$ and $^3H$ mirror nuclei by using
self-consistent iteration procedure and the results are in good agreement with
other theoretical models as well as present available experimental data,
especially the one expected form the proposed 11 GeV Jefferson Laboratory.
