Answer: B
For adults with serious infections, such as bacteremia, infective endocarditis, osteomyelitis, meningitis, pneumonia, and severe skin and soft tissue infection due to MRSA, vancomycin trough concentrations of 15-20 mcg/mL are recommended.
Reference
Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ, Kaplan SL, Karchmer AW, Levine DP, Murray BE, J Rybak M, Talan DA, Chambers HF; Infectious Diseases Society of America.Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children.Clin Infect Dis. 2011 Feb 1;52(3):e18-55. Epub 2011 Jan 4. Weblink here