the functions are:
[tex]\begin{gathered} f(x)=4x^3+3x^2-5x+20 \\ g(x)=9x^3-4x^2+10x-55 \end{gathered}[/tex]Fo the rest will be:
[tex](g-f)(x)=(9x^3-4x^2+10x-55)-(4x^3+3x^2-5x+20)[/tex]now we operate:
[tex]\begin{gathered} 9x^3-4x^3-4x^2-3x^2+10x+5x-55-20 \\ 5x^3-7x^2+15x-75 \end{gathered}[/tex]So is option D
