If I did understand the question right,
We are looking for the intervals where the function f(x) given is increassing.
So as you (should) know (or remember now that I say it : ) f(x) is increasing in an interval if its derivative is Positive (so if f'(x) > 0) So I had try to find the value for f'(x) =0 then look beetween the value of x for f'(x) =0 and see if its positive.
That should get you started.
Hope I helped