Find a polynomial, which, when added to the polynomial 5x^2–3x–9, is equivalent to:
reference
2x−3 show work plz

So you need to turn 5x^2 -3x -9 into 2x - 3. 

Well first you need  to take 5x^2 out by subtracting 5x^2 (-5x^2). 

Then -3x needs to become 2x by adding 5x (+5x). 

Finally -9 needs to become -3 by adding 6 (+6).

Put all the things you did together to make a polynomial.
-5x^2 + 5x + 6