Suppose that $$f(x) = \frac{4 e^x}{4 e^x + 5 }.$$

(A) Find all critical values of $f$. If there are no critical values, enter None. If there are more than one, enter them separated by commas.

Critical value(s) =

(B) Use interval notation to indicate where $f(x)$ is concave up.

Concave up:

(C) Use interval notation to indicate where $f(x)$ is concave down.

Concave down:


(D) Find all inflection points of $f$. If there are no inflection points, enter None. If there are more than one, enter them separated by commas.
Inflection point(s) at $x$ =