I need this 4 questions , thank you so much for your help and you have a great one!!

A 15 Graph of f', the derivative of f a) On what intervals is f decreasing? Justify your answer. b) Identify and label the critical points for f . Justify your answer. c) On what intervals is f concave up? Justify your answer. d) At what values of x does f have points of inflection? Justify your