Tomamos como el límite
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(x^{2} + 6\right)}{- 12 x + \left(x^{2} + 20\right)}\right)$$
cambiamos
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(x^{2} + 6\right)}{- 12 x + \left(x^{2} + 20\right)}\right)$$
=
$$\lim_{x \to 1^+}\left(\frac{\left(x - 3\right) \left(x - 2\right)}{\left(x - 10\right) \left(x - 2\right)}\right)$$
=
$$\lim_{x \to 1^+}\left(\frac{x - 3}{x - 10}\right) = $$
$$\frac{-3 + 1}{-10 + 1} = $$
= 2/9
Entonces la respuesta definitiva es:
$$\lim_{x \to 1^+}\left(\frac{- 5 x + \left(x^{2} + 6\right)}{- 12 x + \left(x^{2} + 20\right)}\right) = \frac{2}{9}$$