A Clinic Uses Doctors and Nurses Optimally and Is Servicing

A clinic uses doctors and nurses optimally and is servicing the maximum number of patients given a limited annual payroll. The last doctor hired treated 1,600 extra patients in a year, while the last nurse hired treated 1,000 extra patients in a year.
-If doctors make $40,000 a year, what do nurses make?

A) $25,000 a year
B) $20,000 a year
C) $15,000 a year
D) $10,000 a year