Find the intervals on which f(x) is increasing, the intervals on which f(x) is decreasing, and the local extrema. 

f(x)=5x^4/7-x^5/7 

Select the correct choice below and, if necessary, fill in the answer box to complete your choice.

 A. The function is increasing on nothing. (Type your answer using interval notation. Use a comma to separate answers as needed.) 

B. There is no solution.