Answer the following questions for the function defined on the interval $[ -16, 18 ]$.

a.) Enter the $x$-coordinates of the vertical asymptotes of $f(x)$ as a comma-separated list. That is, if there is just one value, give it; if there are more than one, enter them separated commas; and if there are none, enter NONE .

b.) $f(x)$ is concave up on the region .
c.) Enter the $x$-coordinates of the inflection point(s) for this function as a comma-separated list.