For the function below, find (a) the critical numbers; (b) the open intervals where the function is increasing; and (c) the open intervals where it is decreasing. f(x) = 2.8 +3.4x - 0.7x2 . . (a) Determine the critical numbers. Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. The critical number(s) is/are (Type an integer or a simplified fraction. Use a comma to separate answers as needed.) O B. There are no critical numbers