Find the value of $x$ at which the function has a possible relative maximum or minimum point. $($Recall that $e^x$ is positive for all $x.)$ Use the second derivative to determine the nature of the function at these

$f(x)=\frac{4-9x}{e^{5x}}$

What is the value of $x$ at which the function has a possible relative maximum or minimum point?

$x=,($Type an exact answer in simplified form.$)$