3. Suppose the joint pdf of lifetimes of a certain part and a spare is given by f(x, y) = e−(x+y), 0 < x < ∞, 0 < y < ∞, and zero otherwise. Find each of the following: (a) The marginal pdf's, f(x) and f(y). (b) The joint CDF, F(x, y). (c) P(X > 2). (d) P(X <Y). (e) P(X + Y > 2).