Consider the function f(x) = 10 r + 4x* + 4. a. Over what interval(s) is f concave up? (If f is never concave up, enter "DNE".) b. Over what interval(s) is f concave down? (If f is never concave down, enter "DNE".) c. f(@) has inflection points at what value(s) of ? (If there are no inflection points, enter "DNE". If f has multiple inflection points, enter the c values as a comma-separated list.) Your work must include a sign-chart to determine concavity