I presume that the function is ??

If that's the case, then

You find the critical points by setting

So you should solve

When you get your [3] critical points, set up a table [which should contain 4 intervals]. Pick a point within each of the intervals you set up and plug them into the derivative. The derivative will either have a positive or negative value at that point. Positive tells you that the function is increasing, and negative tells you that the function is decreasing.

Can you take it from here?

--Chris