Consider the function f(z) = 23 + 4.5x2 - 12x - 2. a) Determine the intervals on which f is concave up and concave down. f is concave up on: f is concave down on: b) Based on your answer to part (a), determine the inflection points of f. Each point should be entered as an ordered pair (that is, in the form (x, y))- (Separate multiple answers by commas.) c) Find the critical numbers of f and use the Second Derivative Test, when possible, to determine the relative extrema. List only the x-coordinates. Relative maxima at: (Separate multiple answers by commas.) Relative minima at: (Separate multiple answers by commas.) (Round to three decimal places at needed.)