$(1$ point$)$ Suppose

$f(x)={\displaystyle \underset{0}{\overset{x}{}}}\frac{t^2-36}{5+co{s}^2(t)}dt$

For what value$($s$)$ of $x$ does $f(x)$ have a local maximum?

$x=$

$($Enter a number, a list of numbers separated by commas, or NONE.$)$