Let's find the inflection points, we'll need to solve the equation for this
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative$$- \frac{2 \left(9 + \frac{9 \left(18 x + 1\right)}{9 x + 1} - \frac{\left(18 x + 1\right)^{2}}{x \left(9 x + 1\right)}\right)}{x^{2} \left(9 x + 1\right)} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections