3. [10pts] Consider the function f (x,y) = x +y on the domain D = {(x, y) l l g x 3 1,0 g y g 3}. (Please write \"NA\" when such points/values do not exist.) (a) f has local minimum values of at the points in D. (b) f has global minimum values of \"_ at the points in D. (c) f has local maximum values of __'___. at the points in D. (d) f has global maximum values of ______ at the points in D