Find the open intervals where the function f(x) = 18x - 18 e ""is concave upward or concave downward. Find any inflection points. Select the correct choice below and, if necessary, fill in the answer box within your choice. O A. The function has a point of inflection at (Type an ordered pair. Type an exact answer in simplified form. Use a comma to separate answers as needed.) O B. The function does not have an inflection point. Select the correct choice below and, if necessary, fill in the answer box(es) within your choice. O A. The function is concave upward on the interval(s) and concave downward on the interval(s) (Type your answers in interval notation. Type exact answers in simplified form. Use a comma to separate answers as needed.) O B. The function is concave downward on the interval(s) . The function is never concave upward (Type your answer in interval notation. Type an exact answer in simplified form. Use a comma to separate answers as needed.) O C. The function is concave upward on the interval(s) The function is never concave downward (Type your answer in interval notation. Type an exact answer in simplified form. Use a comma to separate answers as needed.) O D. The function is never concave upward or downward