Monica Lee, Administrative Director of Digital Imaging Center, has been asked by the practice members to see if it is feasible to add a technologist aide to support the practice's mammography service. The center currently has two digital mammography units and two technologists. She has complied the following information:

Reimbursement per mammogram: $140

Equipment lease per month per machine: $12,000

Equipment maintenance cost per month per machine: $9,000

Technologist cost per mammogram: $35

Technolist aide cost per mammogram: $20

Variable cost per mammogram: 13

What is the patient volume Digital Imaging needs per month to cover fixed and variable costs and to make a $20,000 profit to cover other practice costs?