Explanation:
the point and goal is to come up with a series of multiplications of terms that is equivalent to the original sum of terms.
in doing so, we try to find the same common factors in the sub-groups we are building.
so, the error was to use "-" with the last term, as this "destroyed" the common factor.
it should have been
3x(2x - 3) + 4(2x - 3)
which gives us via the common terms
(2x - 3)(3x + 4)
that is the correct factoring.