Answer: [tex]E) -x^2-13x+15[/tex] .
Step-by-step explanation:
To add : [tex](3x^2 - 5x + 6) + (9 - 8x - 4x^2)[/tex]
[tex]=3x^2 - 5x + 6+ 9 - 8x - 4x^2[/tex]
This can be re-written as :
[tex]3x^2-4x^2-5x-8x+6+9[/tex]
Combine like terms as
[tex]=(3-4)x^2-(5+8)x+15\ \ [\because (-)(+)=(-)]\\\\=-x^2-13x+15[/tex]
Therefore, [tex](3x^2 - 5x + 6) + (9 - 8x - 4x^2)=-x^2-13x+15[/tex]
Hence, the correct option is [tex]E) -x^2-13x+15[/tex] .