I have a mid-term tomorrow and still don't understand this specific concept.

I only know how to do (a-b) I think. Please help with (c)-(f)

Let f(x)=(x^4-18x^2)/5

(a) Use the definition of a derivative or the derivative rules to find f'(x).

My answer: f'(x)= (4x^3-36x)/5

(b) Use the definition of a derivative or the derivative rules to find f' '(x)=

My answer: f' '(x) = (12x^2-36)/5

(c) On what interval is f increasing (include the endpoints in the interval)?

interval of increasing =

(d) On what interval is f decreasing (include the endpoints in the interval)?

interval of increasing =

(e) On what interval is f concave downward (include the endpoints in the interval)?

interval of increasing =

(f) On what interval is f concave upward (include the endpoints in the interval)?

interval of increasing =