Find the absolute maximum and minimum values of f on the set D.f (x,y) = 4xy^2−x^2y^2−xy^3 ;

Find the absolute maximum and minimum values of f on the set D.
f (x, y ) = 4xy2 − x2y2 − xy3 ; D is the closed triangular region in the xy -plane with vertices (0, 0), (0, 6), and (6, 0).