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) = 2x3 -6x2 -90x +7 a) Find the critical number(s). Select the correct answer below and, if necessary, fill in the answer box within 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