Two ballpoint pens are selected at random from a box that contains 3 blue pens, 2 red pens, and 3 green pens. If X is the number of blue pens selected and Y is the number of red pens selected, find (a) the joint probability function f(x, y), (b) P[(X,Y) = A], where A is the region {(x, y)|x + y ≤ 1}.