(1 point} Let f(x) = 12 + 27x x3. Find (a) the intervals on which f is increasing, (b) the intervals on which f is decreasing, (c) the open intervals on which f is concave up, (d) the open intervals on which f is concave down, and (e) the x-coordinates of all inflection points. (a) f is increasing on the interva|(s) (b) f is decreasing on the interva|(s) (c) f is concave up on the open interval(s) (d) f is concave down on the open interval(s) (e) the x coordinate(s) of the points of inflection are Notes: In the first four boxes, your answer should either be a single interval, such as [0.1), a comma separated list of intervals, such as (-inf, 2], (3.4], or the word "none". In the last box, your answer should be a comma separated list of x values or the word "none"