Find the local maximum and minimum values and saddle point(s) of the function. If you have three-dimensional graphing software, graph the function with a domain and viewpoint that reveal all the important aspects of the function. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)

f(x, y) = x³ 108xy + 216y³

(a) local maximum value(s) =

(b) local minimum value(s) =

(c) saddle point(s)(x, y, f)=