Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
$$\lim_{x \to -\infty}\left(2 \log{\left(\frac{3 x}{x} \right)} - 3\right) = -3 + 2 \log{\left(3 \right)}$$
Let's take the limitso,
equation of the horizontal asymptote on the left:
$$y = -3 + 2 \log{\left(3 \right)}$$
$$\lim_{x \to \infty}\left(2 \log{\left(\frac{3 x}{x} \right)} - 3\right) = -3 + 2 \log{\left(3 \right)}$$
Let's take the limitso,
equation of the horizontal asymptote on the right:
$$y = -3 + 2 \log{\left(3 \right)}$$