(1 point) Find the inflection points and local extrema of f(x) = 13 x1/3(x2 - 14). Then find the intervals on which f(x) is concave up and concave down. Inflection points occur at (Enter a comma-separated list of x-coordinates. If there are no inflection points, enter "none".) Local maxima occur at (Enter a comma-separated list of x-coordinates. If there are no local maxima, enter "none".) Local minima occur at (Enter a comma-separated list of x-coordinates. If there are no local minima, enter "none".) f(x) is concave up on f(x) is concave down on