$$(f\bullet g)(x)=f(x)\bullet g(x); =(x+5)\bullet(2x-1); =2x^{2}+9x-5$$
$\left\{\begin{matrix}\\x=0\text{, }y=-5\text{, }z=-5\text{; }x=1\text{, }y=6\text{, }z=6\text{, }&\text{unconditionally}\\x\in \mathrm{R}\text{, }y=\left(2x-1\right)\left(x+5\right)\text{, }z=\left(2x-1\right)\left(x+5\right)\text{, }&g=0\text{ or }f=0\end{matrix}\right.$
