Answer
a) There is one local maximum value which is $0$ at $x=0$, and two local minimum values which are $-13.61$ and $-73.32$ at $x=-1.71$ and $x=3.21$, respectively.
b) The intervals when the function is decreasing are (-∞, -1.71), and (0, 3.21).
The intervals when the function is increasing are (-1.71,0) and (3.21, ∞)
Work Step by Step
a) The local maximum values are all those that are at the top of crests that forms in functions (if any). While the local minimum values are all those that are at the bottom of where U-shaped parts are formed (if any).
b) A function decreases when the slope is negative. While a function increases when the slope is positive.