A cartridge company develops ink cartridges for a printer company and supplies both the ink and the cartridge. The following is the probability mass function of the number of cartridges over the life of the printer.

(a) What is the expected number of cartridges used?

(b) What is the probability that more than six cartridges are used?

(c) What is the probability that 9 out of 10 randomly selected printers use more than 6 cartridges?