What values of $a$ and $b$ make the function $f$ continuous everywhere? $$f(x) = \begin{cases} \displaystyle \frac{x^2-4}{x-2}, &\text{ if } x < 2\\ a x^2 - b x - 12, &\text{ if } 2 \le x < 3\\ 8 x - a + b, &\text{ if } x \ge 3 \end{cases}$$ $a =$ and $b =$