Answer :
Given the initial expression
[tex](-3x^2-9x-3)+(9x^2+x+5)[/tex]Simplify as shown below
[tex]\begin{gathered} \Rightarrow(-3x^2-9x-3)+(9x^2+x+5)=-3x^2-9x-3+9x^2+x+5 \\ =(-3x^2+9x^2)+(-9x+x)+(-3+5) \\ =6x^2-8x+2 \\ \Rightarrow(-3x^2-9x-3)+(9x^2+x+5)=6x^2-8x+2 \end{gathered}[/tex]Therefore, the answer is 6x^2-8x+2