A Dentist's Office, Which Wants to Serve the Maximum Number

Multiple Choice

A dentist's office, which wants to serve the maximum number of patients given a fixed payroll, currently has two dentists and four dental hygienists. Dentists earn $60,000 a year and hygienists earn $15,000 a year. If the office is hiring the optimal combination of dentists and hygienists, and the last dentist hired served 120 additional patients, how many patients will the last hygienist hired add?

A) 30
B) 60
C) 120
D) 240
E) 480