A college is selecting a new server to add in the computing center. The college examines 18 different models, paying attention to the following considerations: A: cartridge tape drive, B: DVD burner, and C: SCSI RAID Array. The number of servers with any or all of these features are as follows: |A| = |B| = |C| = 6, |AN B| = |B N C|=1, |A N C| = 2, |AN BNC | = 0. Answer the following: a) How many of the models have exactly one of the features being considered? b) How many of the models have at least one of the features? c) How many of the models have exactly two of the features? d) How many of the models have at least two of the features?