$\left(fg\right)\left(x\right)=\frac{\sqrt{x}}{17+x}$, Domain: $\left(-\infty,0\right\rbrack$

$\left(fg\right)\left(x\right)=17-\sqrt{x}$, Domain: $\left(0,\infty\right)$

$\left(fg\right)\left(x\right)=\sqrt{x}+17x$, Domain: $\left\lbrack0,\infty\right)$

$\left(fg\right)\left(x\right)=\sqrt{x}\left(x+17\right)$, Domain: $\left\lbrack0,\infty\right)$