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. 4 f( x ) = = -6x- - 216x - 20 (a) The critical number(s) is/are]. Type an integer or a simplified fraction. Use a comma to separate answers as needed.) (b) On which intervals is the function increasing? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. Increasing on (Type your answer in interval notation. Simplify your answer. Use integers or fractions for any numbers in the expression. Use a comma to separate answers as needed.) O B. Never increasing (c) On which intervals is the function decreasing? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. Decreasing on (Type your answer in interval notation. Simplify your answer. Use integers or fractions for any numbers in the expression. Use a comma to separate answers as needed.) O B. Never decreasing