Tomamos como el límite
$$\lim_{x \to 3^+}\left(\frac{- x + \left(x^{2} - 6\right)}{5 - 5 x}\right)$$
cambiamos
$$\lim_{x \to 3^+}\left(\frac{- x + \left(x^{2} - 6\right)}{5 - 5 x}\right)$$
=
$$\lim_{x \to 3^+}\left(\frac{\left(x - 3\right) \left(x + 2\right)}{5 - 5 x}\right)$$
=
$$\lim_{x \to 3^+}\left(- \frac{\left(x - 3\right) \left(x + 2\right)}{5 x - 5}\right) = $$
$$- \frac{\left(-3 + 3\right) \left(2 + 3\right)}{-5 + 3 \cdot 5} = $$
= 0
Entonces la respuesta definitiva es:
$$\lim_{x \to 3^+}\left(\frac{- x + \left(x^{2} - 6\right)}{5 - 5 x}\right) = 0$$