Employees of a large company all choose one of three levels of health insurance coverage, for which premiums, denoted by X, are 1, 2, and 3, respectively. Premiums are subject to a discount, denoted by Y, of 0 for smokers and 1 for non-smokers. The joint probability function of X and Y is given by x2 + 1/2 P(I, y) = for z = 1, 2, 3 and y = 0, 1 31 0, otherwise. Calculate the variance of X - Y, the total premium paid by a randomly chosen employee