We have indeterminateness of type
0/0,
i.e. limit for the numerator is
$$\lim_{x \to 0^+}\left(\sqrt{x + 4} - 2\right) = 0$$
and limit for the denominator is
$$\lim_{x \to 0^+}\left(3 \operatorname{atan}{\left(x \right)}\right) = 0$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to 0^+}\left(\frac{\sqrt{x + 4} - 2}{3 \operatorname{atan}{\left(x \right)}}\right)$$
=
Let's transform the function under the limit a few
$$\lim_{x \to 0^+}\left(\frac{\sqrt{x + 4} - 2}{3 \operatorname{atan}{\left(x \right)}}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{\frac{d}{d x} \left(\sqrt{x + 4} - 2\right)}{\frac{d}{d x} 3 \operatorname{atan}{\left(x \right)}}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{\frac{x^{2}}{3} + \frac{1}{3}}{2 \sqrt{x + 4}}\right)$$
=
$$\lim_{x \to 0^+} \frac{1}{12}$$
=
$$\lim_{x \to 0^+} \frac{1}{12}$$
=
$$\frac{1}{12}$$
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)