5-11. Suppose a fair pair of six-sided dice is tossed and (X,Y) is a bivariate random variable defined on the sample space S = {Ei, i = 1, . . . , 36} . Here each simple eventEi is a point (X = j,Y = j), j = 1, . . . , 6, whereXis the outcome on the first die andYis the outcome on the second die. If the random variable Z = X +Y is the sum of the faces showing, find the probability that X = 3 given Z = 7. What is E (X |Z = 7)?