Find the intervals on which f(x) is increasing, the intervals on which f(x) is decreasing, and the local extrema. f(x) = 3x4 - 84x3 + Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. The function is increasing on (Type your answer using interval notation. Use a comma to separate answers as needed.) OB. There is no solution.