A 58-year-old female presents to clinic for follow-up after recent hospitalization for COPD exacerbation. The patient is currently stable and without acute complaints. She has a 52-pack year smoking history and refuses to be counseled on tobacco cessation. Vital signs are within normal limits. Physical examination reveals a thin female with decreased breath sounds bilaterally and a raspy voice. Osteopathic structural examination reveals decreased movement of ribs 9 and 12 during inhalation. Which of the following is the key rib that treatment should be focused towards?