Tomamos como el límite
$$\lim_{x \to 4^+}\left(\frac{- 5 x + \left(x^{2} + 4\right)}{- 7 x + \left(x^{2} + 6\right)}\right)$$
cambiamos
$$\lim_{x \to 4^+}\left(\frac{- 5 x + \left(x^{2} + 4\right)}{- 7 x + \left(x^{2} + 6\right)}\right)$$
=
$$\lim_{x \to 4^+}\left(\frac{\left(x - 4\right) \left(x - 1\right)}{\left(x - 6\right) \left(x - 1\right)}\right)$$
=
$$\lim_{x \to 4^+}\left(\frac{x - 4}{x - 6}\right) = $$
$$\frac{-4 + 4}{-6 + 4} = $$
= 0
Entonces la respuesta definitiva es:
$$\lim_{x \to 4^+}\left(\frac{- 5 x + \left(x^{2} + 4\right)}{- 7 x + \left(x^{2} + 6\right)}\right) = 0$$