I'll give a hint: You want to find the derivative because clearly that has something to do with increase and decrease. But moreover you want to maximize the increase (and minimize the decrease). Let's first consider the point of fastest increase.
First you need to know where it's increasing, so find those intervals -- presumably you already know how to do this, since the question seems to assume that you already can handle this.
Next, on those intervals, maximize the derivative. That means taking the derivative of the derivative, setting it to zero, and I'll let you fill in the rest.
Make sure that you consider only results at which the function is increasing (i.e. in those intervals you found at the start).
