A junior school subscribes to two different monthly magazine from Ektara publishers, each of which is supposed to arrive in Wednesdays mail. It is likely that each one may arrive on Wednesday, Thursday, Friday or Saturday. Let us suppose that the two arrive independently to one another and for each one P(Wednesday) = 0.3, P(Thursday) = 0.4, P(Friday) = 0.2 and P(Saturday) = 0.1. Let X be a random variable which denotes the number of days beyond Wednesday that it takes for both the magazines to arrive. Find the probability mass function of X