6. (16 points) X and Y are two random variables. Their joint probability density function is: 69'(2x+3y),x :3 o and y 2 0 0, else f(x.y) zl a) (8 points) Find out marginal distribution off(x) and f(y) b) (2 points) Are X and Y independent? 4:} (6 points) Find out P(X > Y)