Answer:
3x-4
Explanation:
The premise is incorrect.
The factorization of 6x^2 -5x -4 is ...
... 6x^2 -5x -4 = (2x +1)(3x -4)
The factor that is not 2x+1 is 3x -4.
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If you were to assume the premise is correct, the x-term of the remaining factor is 6x^2/(2x) = 3x, and the constant term is (-4)/(-1) = +4, suggesting the correct answer to be 3x+4. As we have noted above, this is wrong.
(Have your teacher show you how to work this problem and check the answer.)