A disk drive manufacturer sells storage devices with capacities of one terabyte, 500 gigabytes, and 100 gigabytes with probabilities 0.5, 0.3, and 0.2, respectively. The revenues associated with the sales of the storage devices in that year are estimated to be $50 million, $25 million, and $10 million, respectively. Let X denote the estimated revenue of storage devices during that year. Determine the probability mass function of X.