A function f has f(5) = 21, f'(5) = 1.4, and f''(x) < 0, for x ≥ 5. Which of the following are possible values for f(6) and which are impossible?
(a). f(6) = 21.7 is ?
(b). f(6) = 22.4 is ?
(c). f(6) = 23.8 is ?
Hint: Try to sketch the information given in the problem before answering the questions.