Read this passage from the voting rights act of 1965:

the congress finds that the requirement of the payment of
a poll tax as a precondition to voting (i) precludes persons
of limited means from voting or imposes unreasonable
financial hardship upon such persons as a precondition to
their exercise of the franchise, (ii) does not bear a
reasonable relationship to any legitimate state interest in
the conduct of elections, and (iii) in some areas has the
purpose or effect of denying persons the right to vote
because of race or color. upon the basis of these findings,
congress declares that the constitutional right of citizens
to vote is denied or abridged in some areas by the
requirement of the payment of a poll tax as a precondition
to voting."
according to this excerpt, why was the voting rights act needed to enforce
the fifteenth amendment?