An insurance company offers its policyholders a number of different premium payment options. For a randomly selected policyholder, let X = the number of months between successive payments. The cdf of X is as follows: F ( x ) = 0 0.30 0.41 0.45 0.83 1 x < 1 1 x < 3 3 x < 4 4 x < 6 6 x < 12 12 x (a) What is the pmf of X ? (b) Using just the cdf, compute P ( 3 X 6 ) and P ( 4 X ) . P ( 3 X 6 ) = P ( 4 X ) =.