please help me with this. I have been trying to figure it out for a long time and I need to have dinner with my family very soon.

To subtract this polynomial, we would have to open the bracket
[tex]\begin{gathered} 9x^4+8x^3-6-(5x^2-8x+6) \\ 9x^4+8x^3-5x^2+8x-6-6=9x^4+8x^3-5x^2+8x-12^{} \end{gathered}[/tex]Remember, we only add and subtact directly , Algebraic characters of the same type only
and the same power only.