Vertical Asymptotes of a Rational Function

Factoring shows that $x^2-9=(x-3)*(x+3)$ and $x^2-x-12=(x-4)*(x+3)$; cancelling the common factor $x+3$ yields a removable discontinuity at x = -3, leaving a vertical asymptote at $x=4$.

$x=-3 \text{ and } x=4$

$x=4$

$x=-3$