4. Suppose (X, Y) has joint p.d.f. fx, y (s, t) = le-' He Hit for s, t 2 0. (a) Compute the marginal p.d.f. of X (b) Compute the marginal p.d.f. of Y (c) Are X and Y independent? (d) Compute P{Y = X}. (e) Compute P{Y > X}. (f) Compute P{Y > X + u}. (g) Compute P{Y > X tu | Y > X}