For the function $f(x)=-2 x^3 + 24 x + 3$, find all intervals where the function is increasing: $f$ is increasing on
(Give your answer as an interval or a list of intervals, e.g., (-infinity,8] or (1,5),(7,10) .)

Similarly, find all intervals where the function is decreasing: $f$ is decreasing on
(Give your answer as an interval or a list of intervals, e.g., (-infinity,8] or (1,5),(7,10) .)

Finally, find all critical points in the graph of $f(x)$
critical points: $x =$
(Enter your $x$-values as a comma-separated list, or none if there are no critical points.)