We have indeterminateness of type
0/0,
i.e. limit for the numerator is
$$\lim_{x \to 0^+} \sin{\left(6 x \right)} = 0$$
and limit for the denominator is
$$\lim_{x \to 0^+}\left(- 2 x\right) = 0$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to 0^+}\left(\frac{\left(-1\right) \sin{\left(6 x \right)}}{2 x}\right)$$
=
Let's transform the function under the limit a few
$$\lim_{x \to 0^+}\left(- \frac{\sin{\left(6 x \right)}}{2 x}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{\frac{d}{d x} \sin{\left(6 x \right)}}{\frac{d}{d x} \left(- 2 x\right)}\right)$$
=
$$\lim_{x \to 0^+}\left(- 3 \cos{\left(6 x \right)}\right)$$
=
$$\lim_{x \to 0^+} -3$$
=
$$\lim_{x \to 0^+} -3$$
=
$$-3$$
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)