Gaya APA

Foster, D, L., O'Keefe, C. (1990). The Business of Travel : Agency Operations and Administrasi . USA: McGRAW-HILL.

Gaya MLA

Foster, Dennis, L.., O'Keefe, Carole. "The Business of Travel : Agency Operations and Administrasi". USA: McGRAW-HILL, 1990. Text.