4.4.6 We have three dice, each with numbers z = 1, . . . , 6 , and with probabilities as follows: die 1: p ( z ) = 1/6, die 2: p ( z ) = (7 - z)/21, die 3: p ( z ) = z2/91. A die is selected, tossed, and the number 4 appears. What is the probability that it is die 2 that was tossed?