Tính \(\mathop {\lim }\limits_{x \to 6} \frac{{{x^2} - 9x + 18}}{{42 - 7x}}\).

Câu hỏi :

Tính \(\mathop {\lim }\limits_{x \to 6} \frac{{{x^2} - 9x + 18}}{{42 - 7x}}\).