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(Short) Polynomials Q please help!

Have a C4 paper tomorrow but there's one thing that just came up in a past paper that I simply don't get.

Basically it's showing that (4x³-11x-3) can be written as (2x+3)(ax²-bx-c)
And the answer is (2x+3)(2x²-3x-1)How do you get that? I kind of see that the last terms (+3and -1) would multiply to give the required -3, and the 2x and 2x²wouldmultiply and give the required -11x, but what about “b”? How do you get “-3x”?
It leads onto "find all solutions" Q so it would cost a lot of marks!