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$$- \frac{9 \left(\frac{1}{\left(3 x + 11\right)^{\frac{3}{2}}} + \frac{1}{\left(3 x - 5\right)^{\frac{3}{2}}}\right)}{4} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections