Yeah so for B, since you have found the zeros of f'(x), you can then determine at which interval(s) of x (or at what x-values) that the range is smaller than zero (because at this point the graph of f has a relative min). Remember to compare with the (0,2] interval so that you can only take those x-values within the interval.
P/s: It is super hard for me to just write like that without anything to illustrate. Hope you understand :))