Answer
$(-\infty, +\infty); x \ne -6, 3$
Work Step by Step
In order to find when the function given exists, we have to find when it is undefined. Thus, we see when the bottom of the fraction is equal to 0:
$$x^2 +3x -18 = 0 \\ (x+6)(x-3)=0 \\ x=-6, 3$$
Thus, the domain is:
$(-\infty, +\infty); x \ne -6, 3$
