Tomamos como el límite
$$\lim_{x \to 6^+}\left(\frac{3 x + \left(x^{2} + 7\right)}{- 3 x^{2} + \left(x^{4} + 4\right)}\right)$$
cambiamos
$$\lim_{x \to 6^+}\left(\frac{3 x + \left(x^{2} + 7\right)}{- 3 x^{2} + \left(x^{4} + 4\right)}\right)$$
=
$$\lim_{x \to 6^+}\left(\frac{x^{2} + 3 x + 7}{x^{4} - 3 x^{2} + 4}\right)$$
=
$$\lim_{x \to 6^+}\left(\frac{x^{2} + 3 x + 7}{x^{4} - 3 x^{2} + 4}\right) = $$
$$\frac{7 + 3 \cdot 6 + 6^{2}}{- 3 \cdot 6^{2} + 4 + 6^{4}} = $$
= 61/1192
Entonces la respuesta definitiva es:
$$\lim_{x \to 6^+}\left(\frac{3 x + \left(x^{2} + 7\right)}{- 3 x^{2} + \left(x^{4} + 4\right)}\right) = \frac{61}{1192}$$