Cho đa thức \(f\left( x \right)\) thoả mãn \(\mathop {\lim }\limits_{x \to 2} \frac{{f\left( x \right) - 20}} = 10.\) Tính \(\mathop {\lim }\limits_{x \to 2} \frac{{\sqrt[3]{{6f\left( x \right) + 5}} - 5}}{{{x^2} + x - 6}}\).