We have indeterminateness of type
oo/oo,
i.e. limit for the numerator is
$$\lim_{x \to \infty}\left(\log{\left(x \right)} + \log{\left(3 \right)}\right) = \infty$$
and limit for the denominator is
$$\lim_{x \to \infty} x^{2} = \infty$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to \infty}\left(\frac{\log{\left(3 x \right)}}{x^{2}}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\frac{d}{d x} \left(\log{\left(x \right)} + \log{\left(3 \right)}\right)}{\frac{d}{d x} x^{2}}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{1}{2 x^{2}}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{1}{2 x^{2}}\right)$$
=
$$0$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 1 time(s)