Help please!

For the following function, find (a) the critical numbers; (b) the open intervals where the function is increasing; and (c) the open intervals where the function is decreasing f(x) = xe-9x (a) Find the critical number(s). First find f' (x). F' (x ) = 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 (Use a comma to separate answers as needed.) O B. There are no critical numbers for this function. (b) Find the open intervals where the function is increasing. Select the correct choice below and, if necessary, fill in the answer box to complete your choice O A. The function is never increasing. O B. The function is increasing on the open interval(s) (Type your answer in interval notation. Simplify your answer. Use integers or fractions for any numbers in the expression. Use a comma to separate answerssas needed.) (c) Find the open intervals where the function is decreasing. Select the correct choice below and, if necessary, fill in the answer box to complete your choice