Find the intervals on which f(x) is increasing, the intervals on which f(x) is decreasing, and the local extrema.
f(x)=3x⁴+36x³+26
Select the correct choice below and, if necessary, fill in the answer box to complete your choice.
A. The function is increasing on ___________ (Type your answer in interval notation. Type integers or simplified fractions. Use a comma to separate answers
as needed.)
B. The function is never increasing.