Consider the following function.
$f(x) = (4 - x)e^{-x}$
(a) Find the intervals of increase or decrease. (Enter your answers using interval notation.)
increasing
decreasing
(b) Find the intervals of concavity. (Enter your answers using interval notation. If an answer does not exist, enter DNE.)
concave up
concave down
(c) Find the point of inflection. (If an answer does not exist, enter DNE.)
$(x, y) = (\quad)$