For the following function, a) give the coordinates of any critical points and classify each point as a
relative maximum, a relative minimum, or neither; b) identify intervals where the function is increasing
or decreasing; c) give the coordinates of any points of inflection; d) identify intervals where the function is
concave up or concave down, and e) sketch the graph.
$h(x) = 5x^3 - 15x$