hello
this question can be referred to as a function of function
[tex]\begin{gathered} f(x)=2x+8 \\ g(x)=-4x-20 \\ f\mathrm{}g=(2x+8)(-4x-20) \\ f\mathrm{}g=8x^2-40x-32x-160 \\ f\mathrm{}g=8x^2-72x-160 \\ we\text{ can divide through by 8} \\ f\mathrm{}g=x^2-9x-20 \end{gathered}[/tex]