For the function below, find $($a$)$ the critical numbers; $($b$)$ the open intervals where the function is increasing; and $($c$)$ the open intervals where it is decreasing.

$f(x)=\frac{4}{3}{x}^3-2x^2-24x-32$

$($a$)$ Determine the critical numbers. Select the correct choice below and, if necessary, fill in the answer box to complete your choice.

A$.$ The critical number$($s$)$ is$/$are

$($Type an integer or a simplified fraction. Use a comma to separate answers as needed.$)$

B$.$ There are no critical numbers.