Consider two urns, urn A and urn B. In urn A, there are 3 balls numbered 0,1,2. In urn B there are 6 balls numbered 1,2,3,4,5,6. A ball is drawn from urn A, then a ball is drawn from urn B. Define X A as the number of the ball from urn A and X B the number of the ball drawn form urn B.