What is the probability there are exactly 2 customers in line in a two-server model?

How would you cite different books by the same author on the works cited page? moore, jack h. folk songs and ballads. salem: poetry press, 1999. print. moore, jack h. ballads in poetry – a critical review. dallas: garden books, 1962. print. moore, jack h. folk songs and ballads. salem: poetry press, 1999. print. –––. ballads in poetry – a critical review. dallas: garden books, 1962. print. moore, jack h. ballads in poetry – a critical review. dallas: garden books, 1962. print. moore, jack h. folk songs and ballads. salem: poetry press, 1999. print. moore, jack h. ballads in poetry – a critical review. dallas: garden books, 1962. print. –––. folk songs and ballads. salem: poetry press, 1999. print.